CBSE Class 9

Extra Questions for Class 9 English: Here we are providing NCERT Extra Questions for Class 9 English Beehive, Moments, English Literature Reader. Students can get Class 9 English NCERT Solutions, Chapter Wise CBSE Class 9 English Important Questions and Answers were designed by subject expert teachers.

You can refer to NCERT Solutions for Class 9 English Beehive, Moments, Literature Reader to revise the concepts in the syllabus effectively and improve your chances of securing high marks in your board exams.

Class 9 English Important questions with answers for all lessons are provided here on this page. These extra questions are very beneficial for your exam preparation. As it enhances your understanding level, knowledge about the concept, speed, accuracy & time management skills. So, practicing some extra important questions prescribed by NCERT for Class 9 English is mandatory to attain good scores in the final board examination.

Extra Questions for Class 9 English Beehive, Moments, Literature Reader Important Questions

By accessing the following pdf links you can easily view & downlaod extra questions for class 9 English with solutions that will be useful to ace up your exam preparation.

Extra Questions for Class 9 English Literature Reader

1. How I Taught My Grandmother to Read Extra Questions
2. A Dog Named Duke Extra Questions
3. The Man Who Knew Too Much Extra Questions
4. Keeping it from Harold Extra Questions
5. Best Seller Extra Questions
6. The Brook Extra Questions
7. The Road Not Taken Extra Questions
8. The Solitary Reaper Extra Questions
9. Lord Ullin’s Daughter Extra Questions
10. The Seven Ages Extra Questions
11. Oh, I Wish I’d Looked After Me Teeth Extra Questions
12. Song of the Rain Extra Questions
13. Villa for Sale Extra Questions
14. The Bishop’s Candlesticks Extra Questions
15. Gulliver’s Travels Questions and Answers
16. Three Men in a Boat Question and Answers

Extra Questions for Class 9 English Beehive Prose

1. The Fun They Had Extra Questions
2. The Sound of Music Extra Questions
3. The Little Girl Extra Questions
4. A Truly Beautiful Mind Extra Questions
5. The Snake and the Mirror Extra Questions
6. My Childhood Extra Questions
7. Packing Extra Questions
8. Reach for the Top Extra Questions
9. The Bond of Love Extra Questions
10. Kathmandu Extra Questions
11. If I Were You Extra Questions

Extra Questions for Class 9 English Beehive Poem

1. The Road Not Taken Extra Questions
2. Wind Extra Questions
3. Rain on the Roof Extra Questions
4. The Lake Isle of Innisfree Extra Questions
5. A Legend of the Northland Extra Questions
6. No Men are Foreign Extra Questions
7. The Duck and the Kangaroo Extra Questions
8. On Killing a Tree Extra Questions
9. The Snake Trying Extra Questions
10. A Slumber did my Spirit Seal Extra Questions

Extra Questions for Class 9 English Moments

1. The Lost Child Extra Questions
2. The Adventures of Toto Extra Questions
3. Iswaran the Storyteller Extra Questions
4. In the Kingdom of Fools Extra Questions
5. The Happy Prince Extra Questions
6. Weathering the Storm in Ersama Extra Questions
7. The Last Leaf Extra Questions
8. A House is not a Home Extra Questions
9. The Accidental Tourist Extra Questions
10. The Beggar Extra Questions

If you have any doubts or questions regarding NCERT Extra Questions for Class 9 English Beehive, Moments, English Literature Reader, you can reach out to us in the comment section below and we will get back to you as soon as possible.

Chapter 13 Why Do we Fall Ill Class 9 Science Important Questions with Answers PDF will help you in scoring more marks in your exams.

Why Do we Fall Ill Class 9 Important Questions Science Chapter 13

Very Short Answer Questions

Question 1.
Name the disease that can be caused by UV radiations.
(CCE 2011)
Answer:
Skin cancer.

More Resources

• Previous Year Question Papers for CBSE Class 9 Science
• NCERT Solutions for Class 9 Science
• NCERT Exemplar Solutions for Class 9 Science
• Value Based Questions in Science for Class 9
• HOTS Questions for Class 9 Science

Question 2.
Why does intake of penicillin not affect human cells. ?
(CCE 2014)
Answer:
Penicillin inhibits the formation of cell wall which is present in bacteria but is absent around human cells.

Question 3.
What is symptom of a disease ? (CCE 2014)
Answer:
Sympton of a disease is manifestation of a structural or func¬tional change in the body, e.g., cough, fever, diarrhoea.

Question 4.
You have suffered from chicken pox when you were in class three. Why will you not suffer from it again ?
(CCE 2014, 2015)
Answer:
A single chicken pox infection gives life long immunity as the memory cells and specific antibodies remain active throughout the life of a person.

Question 5.
How does infection spread from an unhealthy person to a healthy person ? (CCE 2015)
Answer:
Direct contact, air, fomite or vector.

Question 6.
The immediate causes of many diseases are not infectious.
Name any two such diseases. (CCE 2015)
Answer:
Diabetes, hypertension, cancer.

Question 7.
Which type of disease causes more damage to our body — acute or chronic and why ? (CCE 2015)
Answer:
Chronic disease causes more harm to the body as it is of longer duration and damages the affected organs.

Question 8.
Name one organ each affected by :

1. Malaria
2. Tuberculosis. ( CCE 2015)

Answer:

1. Malaria Liver, RBCs, Spleen.
2. Tuberculosis Lungs.

Question 9.
Why do female mosquitoes need highly nutritions food in the form of human blood ? (CCE 2016)
Answer:
Blood provides nutrients required for egg laying by the female mosquito.

Question 10.
Name the disease caused by Trypanosoma. (CCE 2016)
Answer:
Sleeping sickness.

Question 11.
Name any two diseases caused by protozoa. (CCE 2016)
Answer:
Sleeping sickness (Trypanosoma), Malaria (Plasmodium).

Short Answer Questions (2 Marks)

Question 1.
(a) What is an epidemic disease ?
(b) Which organ is affected if a person is suffering from jaundice ? (CCE 2011, 2012)
Answer:
(a) An epidemic disease is the one which spreads rapidly and extensively affecting many individuals simultaneously in a particular area. It is usually an infectious disease, e.g., encephalitis, malaria, dengue,
(b) Liver.

Question 2.
State two consequences which one has to face while dealing with an infectious disease. (CCE 2011)
Answer:

1. Tissue damage and deranged body functions requiring rest and care to recover.
2. A person suffering from an infectious disease can be a source for spread of disease to other persons.

Question 3.
If your friend is suffering from malaria, what are your chances of catching malaria ? (CCE 2011, 2012)
Answer:
Little chance. Malaria is an infectious disease which is spread by the bite of an infected female Anopheles mosquito. The vector is mostly active during night, that also if it is present in the room of your friend when you are visiting him.

Question 4.
(a) What are vectors ?
(b) In many species of mosquitoes, the males do not prefer blood, but females do. State why ?
(CCE 2012)
Answer:
(a) Vectors: They are organisms which spread the pathogens from an infected person to a healthy person, e.g., sandfly, female mosquitoes.
(b) The female mosquitoes of many species require human/ animal blood meal in order to obtain nutrients for laying eggs.

Question 5.
(a) Write any biochemical pathway in bacteria that is blocked by antibiotics like penicillin.
(b) Whv is it difficult to make antiviral drugs ? (CCE 2012)
Answer:
(a) Penicillin blocks cell wall formation in bacteria.
(b) Viruses have very few biochemical pathways of their own so that drugs for their disruption are not easy to manufacture.

Question 6.
What causes encephalitis ? How does it enter the body. Which organ does it infect ? What are the symptoms, if this organ is infected ? (CCE 2012)
Answer:
Cause. Encephalitis is generally caused by virus, e.g., JEV in case of Japanese encephalitis.
Entrance. The virus enters the body through the bite of infected mosquito like female Culex.
Organ Infected. Brain.
Symptoms. Inflammation of brain and its membrane causing severe rigors, altered mental status, seizures, severe headache, stiff neck and bulgings in fontanelles of skull. A vaccine is available against the disease.

Question 7.
Which of the following diseases will cause major ill effects on general health—elephantiasis, cough and cold, tuberculosis, diarrhoea ? (CCE 2012)
Answer:
Encephalitis and tuberculosis cause major ill effects on health because they are chronic diseases.

Question 8.
Name two bacterial disease that spread through contaminated water. (CCE 2012)
Answer:
Cholera, typhoid.

Question 9.
Apart from sexual contact, AIDS virus can be spread by which other means ? (CCE 2012)
Answer:

1. Contaminated needles, syringes and tatooing.
2. Blood transfusion from infected person.

Question 10.
A person is suffering from chest pain, breathlessness, loss of body weight, persistent cough and produces stained sputum. Name the disease. (CCE 2012)
Answer:
Tuberculosis.

Question 11.
(a) Name a worm which is found in our small intestine.
(b) Name the bacteria which can cause acne.
(c) Which protozoan is responsible for sleeping sickness.
(d) Which disease is caused by protozoan Leishmania.
(CCE 2012)
Answer:
(a) Worm. Ascaris lumbricoides.
(b) Acne. Staphylococcus. Ans.
(c) Sleeping Sickness. Trypanosoma gambiense.
(d) Leishmania donovani. Kala-azar or black fever.

Question 12.
(a) List the causative organisms for AIDS.
(b) Name two fungal diseases. (CCE 2012)
Answer:
(a) HIV or human immunodeficiency virus.
(b) Ringworm, athlete’s foot, barber’s itch.

Question 13.
What is parasite ? Give two examples.
(CCE 2012, 2013)
Answer:
Parasite. It is an organism that obtains its food from a living organism of another species for a part or whole of its life, e.g., Plasmodium (malaria parasite). Vibrio cholerae (cholera causing bacterium).

Question 14.
Write two examples each of
(a) Viral diseases
(b) Bacterial
diseases. (CCE 2012)
Answer:
(a) Viral Diseases: Common cold, Influenza, AIDS.
(b) Bacterial Diseases: Typhoid, Cholera, Acne.

Question 15.
What are infectious diseases ? Write rwo ways by which they can be controlled. (CCE 2012, 2013)
Answer:
Infectious diseases are those diseases which are caused by pathogens that can pass from an infected person to a healthy one.
Control,

1. Symptomatic treatment.
2. Killing the infectious agent.

Question 16.
“Community health is essential for good individual health”.
Justify this statement by giving examples. (CCE 2012)
Answer:
Community health is helpful in maintaining good individual health by

1. Proper removal of garbage.
2. Drainage and sewage services.
3. Proper drinking water.
4. Vector and pest control.
5. Unadulterated food articles.
6. Vaccination and other health services.
7. Harmonious social interactions.

Question 17.
List any two ways of preventing the spread of air borne diseases.
Answer:

1. Avoiding visiting over-crowded places.
2. Avoiding coming close to a person suffering from an air borne disease.

Question 18.
Chances of spreading cholera are higher in a village. reason. (CCE 2012)
Answer:
Cholera spreads through contaminated food and water. In villages, the drinking water is seldom treated. The village ponds are likely to become contaminated as it is used for washing, bathing of animals as well as humans. In some areas pond water is used for drinking as well.

Question 19.
AIDS is a fatal disease. Explain why ? (CCE 2012)
Answer:
In AIDS, the immune system of the patient becomes weak because HIV destroys helper T-cells of the body. The patient loses the power to fight minor infections with common cold becoming pneumonia or a minor gut infection causes diarrhoea with blood loss. These opportunistic infections kill the patient.

Question 20.
Influenza or common cold spreads faster and is difficult to control. Explain. (CCE 2012)
Answer:
Influenza or common cold spreads as droplets through air infecting nearly every body coming in near contact with the patient. All the latter will spread the disease to many more persons and so on.
The disease is difficult to control as antibiotics are infective because the disease is viral in nature.

Question 21.
“Being disease free is not the same as being healthy.” Explain the above statement giving an example. (CCE 2012)
Answer:
Disease free person is the one who does not have any discomfort or derangement in any part of the body. A healthy person is one who is in a state of complete, physical, mental and social well being. For example, a dancer may be disease free but in poor health if one is unable to perform as per requirement.

Question 22.
Explain why some children fall ill more frequently than others living in the same locality. (CCE 2012)
Answer:
The children who fall ill more frequently might be having

1. Poor health due to undernourishment
2. Unhygienic conditions around them
3. Poor heredity.

Question 23.
Explain how individual health depends upon social and mental well being. (CCE 2012)
Answer:
Disease is related to individual sufferers but health includes not only disease free but also social and mental well being. Social well being includes good public health services, proper earning and social harmony. Any insufficiency leads to defective health. Similarly, mental health like freedom from depression and anxiety are essential for our optimum and joyful life at work, studies, home and social gatherings.

Question 24.
Although Archana has been suffering from cold and cough, she decided to appear for her class test. Classmates seated close to her had an exposure to the infection being carried by Archana. However, only one of them actually suffered from cold and cough. Explain what prevented rest of her classmates catching cold and cough. (CCE 2012)
Answer:
For catching a disease a person should

1. Receive an infective dose of pathogen
2. Have lower immunity. Every body sitting near Archana did not receive equal infective dose nor their immunity was weak.

Question 25.
State mode of transmission of
(a) Syphilis
(b) Tuberculosis
(c) Jaundice
(d) Japanese encephalitis. (CCE 2012)
Answer:
(a) Syphilis. Sexual contact.
(b) Tuberculosis. Droplets through air.
(c) Jaundice. Contaminated water.
(d) Japanese Encephalitis. Bite of infected female mosquito Culex.

Question 26.
State any four ways by which AIDS virus spreads from an infected person to a healthy person. (CCE 2013)
Answer:

1. Unprotected sexual contact with an infected person,
2. Common needles and syringes.
3. Transfusion of infected blood.
4. Transplacental transmission.

Question 27.
Name the triple vaccine which saves the life of babies from three diseases.
Answer:
DPT or vaccine against Diphtheria, Pertussis (Whooping Cough) and Tetanus.

Question 28.
State the method of transmission of each of the following diseases :
(a) Tuberculosis
(b) Cholera
(c) Malaria
(d) AIDS.
(CCE 2013)
Answer:
(a) Tuberculosis—Droplets through air.
(b) Cholera—Contaminated food and water.
(c) Malaria—Female Anopheles.
(d) AIDS—Sexual and blood contact.

Question 29.
What causes Japanese encephalitis ? How it can be prevented ? (CCE 2014)
Answer:
It is caused by JEV or Japanese Encephalitis Virus through bite of infected Culex mosquito.
Prevention,

1. Vaccination,
2. Protection from mosquito bite like gauze wire double doors and windows, mosquito repellents, mosquito nets and elimination of nearby breeding places of mosquitoes.

Question 30.
State two principles of treatments. (CCE 2014)
Answer:

1. Reduce the effect of disease by giving symptomatic treatment and bed rest.
2. Killing of infectious agents through drugs.

Question 31.
Explain what is organ specific manifestation. (CCE 2014)
Answer:
It is adaptation of pathogens to infect particular organs of the body. Organ specific manifestation is of two types, portal related. (e.g., lungs for nasal entry in case of pneumonia and tuberculosis) and nonportal organs {e.g., Plasmodium passing into liver and then erythrocytes in blood).

Short Answer Questions (3 Marks)

Question 1.

1. Differentiate between acute and chronic diseases.
2. Give one example each of acute and chronic diseases,
3. Mention any two causes of baby’s disease.
   (CCE 2011, 2012, 2013)

Answer:

1. An acute disease is of shorter duration which causes little damage to the body. A chronic disease is of longer duration which damages the body system affected by it.
2. Example. Acute Disease. Diarrhoea, Typhoid. Chronic Disease. Tuberculosis, Diabetes.
3. Baby’s Disease,
   1. Poor improper nourishment.
   2. Contaminated air, water, food.

Question 2.
(i) Match the columns with correct options

(ii) Name any one disease when the microbes target
(a) Liver
(b) Lungs. (CCE 2011)
Answer:
(i) (a) Fungal disease— Skin disease,
(b) Viral disease— Dengue fever
(c) Protozoan disease— Malaria
(d) Bacterial disease— Cholera.
(ii) (a) Liver—Jaundice,
(b) Lungs—Pneumonia.

Question 3.
(i) Give definition of ‘health’.
(ii) State and explain in brief the four major factors which are the causes of disease. (CCE 2011)
Answer:
(i) Health is a state of complete physical, mental and social well being that enables one to lead a socially and economically productive life (WHO, 1978).
(ii) Causes of Disease:

1. Pathogens: Many bacteria, viruses, fungi, protozoans and worms produce diseases, spreading from an infected
   person to healthy one through various means of transport, e.g., Malaria, Diarrhoea, TB.
2. Deficiency: Nutrient deficiency including that of minerals and vitamins, leads to several diseases like marasmas, kwashiorkor, pellagra, goitre, anaemia.
3. Genetic Disorders: Caused by defective heredity, e.g., haemophilia.
4. Degenerative Disorders: Natural defects appearing due to senescence, e.g., hypertension, atherosclerosis, arthritis.

Question 4.
(i) Match the following columns with correct answers

(ii) “High blood pressure can be caused by excessive weight and lack of exercise”. Justify the statement.
(CCE 2011)
Answer:
(i) (a) Leishmanh— Kala-azar
(b) Staphylococcus— Acne,
(c) Trypanosoma— Sleeping sickness
(d) Ascaris lumbricoides— Worm.
(ii) Excessive weight and lack of exercise results in development of more body mass that will cause the formation of more blood vessels and hence more blood supply. It will put pressure on heart to pump more blood.

Question 5.
(a) Which of the following diseases are protozoan in origin : Dengue, Malaria, Kala-azar, HIV-AIDS.
(b) Suggest any two ways to prevent being infected by protozoa. (CCE 2011)
Answer:
(a) Malaria, Kala-azar.
(b)

1. Protection from vectors (mosquito and sand fly in the above two cases).
2. Proper waste disposal and non-accumulation of stagnant water.

Question 6.
(a) Write a few common signs and symptoms of the disease if brain is affected.
(b) Give one local and one general effect of inflammation process. (CCE 2011)
Answer:
(a) Headache, vomiting or fits and unconsciousness.
(b) Local Effect. Pain, redness, swelling. General Effect. Fever.

Question 7.
(a) Which part of the body is infected by malaria causing microbe ?
(b) What are the two ways to treat an infectious disease ? (CCE 2011)
Answer:
(a) Liver, followed by red blood corpuscles.
(b)

1. Reduce the effect of disease by symptomatic treatment and rest.
2. Killing the pathogen by medicine.

Question 8.
(a) Doctors diagnosed that Radha was suffering from HIV-AIDS. List any two methods by which she might have contacted the disease. Name the organ affected by this disease.
(b) Why antibiotics cannot be used for its treatment ? Justify your answer. (CCE 2011)
Answer:
(a)

1. Transfusion of infected blood.
2. Use of infected syringe, blade, razor or tattooing. Organ Affected. Lymph nodes.

(b) HIV-AIDS is a viral disease. Antibiotics have no role in treating viral diseases because viruses have no metabolic machinery of their own (which can be disrupted by an antibiotic).

Question 9.
Ravi suffered from tuberculosis while Rehman suffered from typhoid. Which disease caused more damage and why ? (CCE 2011, 2012)
Answer:

1. Tuberculosis is a chronic disease while typhoid is an acute disease.
2. Chronic disease takes a long time to get cured. It causes damage to the affected organ and other parts of the body. Acute disease of typhoid lasts for a shorter duration and causes little damage to the body.

Question 10.
(a) If a person is suffering from jaundice, name the mode of its transmission and the organ affected by this disease.
(b) List one general mode of prevention of jaundice.
(c) It has been observed that despite the availability of vaccine for hepatitis A in the market, it may not be necessary to be given to children by the time they are 5 years old. Why ? (CCE 2011)
Answer:
(a) Jaundice (yellowness of sclera of eyes and skin) is commonly spread by contaminated water and food in case of hepatitis A. The organ affected is liver.
(b) Mode of Prevention. Eating hygienic food and drinking disinfected water (by chlorination, boiling or ozonisation)
(c) Hepatitis being a viral infection, is self limited by the body defences. Commonly the children have suffered a bout of hepatitis A by the time they reach the age of 5. Therefore, they have become immune to this hepatitis and do not need vaccine for the same.

Question 11.
What is human immune system ? What is a vaccine ? How immunisation can be achieved ? (CCE 2011)
Answer:

1. Human immune system is made of two types of lymphocytes, T-lymphocytes and B-lymphocytes. They kill the invading microbes. The killed microbes are removed by phagocytes.
2. Vaccine: It is preparation containing heat killed or chemically weakend pathogen or its surface coating that functions as antigen.
3. Achievement/Basis of Immunisation: Development of immunity or resistance against a pathogen is called immunisation. It develops when a pathogen or its antigen comes in contact with the immune system of the body. The immune system develops specific T-lymphocytes and B-lymphocytes to immobilise and kill the pathogen. Certain T-lymphocytes called memory cells also remain in the body for a long time. Whenever, the same pathogen enters the body later on, the memory cells help to quickly produce T and B-lymphocytes specific for that pathogen and eliminate the same vigorously.

Question 12.
List any two differences between infectious and non- infectious diseases. Write any one example of each disease.
(CCE 2011)
Answer:
Differences Between Infectious and Non-infectious Diseases

Question 13.
(a) Which system of our body is activated in response to infection and how it responds ?
(b) Explain how HIV-AIDS virus affects and damages our body. (CCE 2011, 2012)
Answer:
(a) The body system activated in response to an infection is immune system. It responds to an infection by producing T-lymphocytes and B-lymphocytes that immobilise and kill the pathogen.
(b) HIV-AIDS virus attacks and multiplies inside T- lymphocytes of the immune system. With the reduction in the number of T-lymphocytes the immune system of the body becomes so weak that the body is unable to fight off even minor infections. Common cold can become pneumonia or minor intestinal infection can turn into prolonged diarrhoea with blood loss. These minor infections become so strong as to kill the HIV-AIDS infected person.

Question 14.
What are the principles of treatment of a disease ? (CCE 2011, 2012)
Answer:
There are two ways to treat an infectious disease. They are

1. Reduce the Effect of Disease by
   1. Symptomatic treatment like use of antipyretic, analgesic, antidiarrhoeal or antiallergic medicine,
   2. Bed rest.
2. Killing the Infectious Agent. After proper diagnosis of the pathogen, pathogen specific medicine is given to kill the same. Antibiotic medicines are available for killing bacterial pathogens. Similarly anti-fungal anthelmintic and antiprotozoan medicines are also available. However, very few antiviral medicines are available as viruses do not have any metabolic machinery of their own (which can be attacked by any medicine).

Question 15.
(a) Name two diseases for which the children below the age of one year should be vaccinated.
(b) What are symptoms shown by a person if

1. Lungs get infected
2. Stomach is infected ? (CCE 2011)

Answer:
(a) DTP-Hib. Against diphtheria, tetanus, pertussis and influenza type B.
(b)

1. Lungs: Cough, breathlessness due to blocking of alveoli and bronchioles.
2. Stomach: Stomach-ache, vomiting, nausea, loss of appetite as stomach is the organ where sensation of hunger starts.

Question 16.
(a) A hefty boy of 12 years often picks up fight with others. Do you think he is in good health ? If so, then explain your answer.
(b) Give an example of the disease caused by

1. Protozoa
2. Bacterium
3. Virus
4. Worm. (CCE 2011)

Answer:
(a) The hefty boy is neither physically nor mentally healthy. He is over weight due to excessive eating habit. May be he is also not doing exercise. Picking up quarrels indicates his mental sickness.
(b)

1. Protozoan: Malaria,
2. Bacterial: Typhoid.
3. Viral: HIV-AIDS.
4. Worm: Ascariasis.

Question 17.
(a) Mention two factors on which severity of disease manifestation depends.
(b) Once you have been infected by small pox, there is no chance of suffering from it again. Give reason.
(c) Mention two ways of preventing disease.
(CCE 2011)
Answer:
(a) Severity of disease manifestation depends upon two factors :

1. Number of microbes over and above the ineffective dose.
2. Health status of the person.

(b) Certain viral diseases are one time affair, e.g., small pox, hepatitis A. The single infection activates the immune system, producing pathogen specific T-lymphocytes, B-lymphocytes and memory T-lymphocytes. After the recovery from the disease the memory lymphocytes persist in the body for life. In case of a second infection, the memory lymphocytes produce a large number of immune cells to immediately kill and dispose off the pathogen.
(c)

1. Sanitation and disinfected drinking water.
2. Hygiene.
3. Vaccination where available.

Question 18.
Mention the symptoms because of which you will visit the doctor and why ? (CCE 2011)
Answer:
Cough, cold, loose motions, pain in abdomen, headache, wound with pus, continuous pain in some body part, breathlessness, loss of body weight, feeling of tiredness. Each symptom can be due to many reasons. Only a doctor can diagnose the ailment and prescribe proper treatment.

Question 19.
Identify the diseases which spread through the following means ? Also name the target organs,
(a) Sexual contact
(b) Mosquitoes
(c) Air. (CCE 2011)
Answer:
(a) Sexual Contact: HIV-AIDS. Immune system (T- lymphocytes).
(b) Mosquitoes: Malaria. Liver, RBCs.
(c) From Air Via Nose: Tuberculosis. Lungs.

Question 20.
What would be the symptoms if the microbes infect the following targets :
(a) Lungs
(b) Liver
(c) Brain ?
(CCE 2011, 2012)
Answer:
(a) Lungs: Cough, breathlessness
(b) Liver: Jaundice
(c) Brain: Headache, vomiting, fits or unconsciousness.

Question 21.
Suggest three ways to prevent spreading of infectious communicable diseases. (CCE 2011, 2012, 2016)
Answer:

1. Public Health Measures: Prevention of overcrowding, sanitation and disinfected drinking water.
2. Personal Health Measures: Personal and domestic hygiene, proper nutrition, rest and exercise.
3. Immunisation: Vaccination wherever available.
4. Nutrition: A proper balanced diet keeps a person in good health.

Question 22.
How principle of immunisation is being implemented for eliminating polio ? (CCE 2011)
Answer:
Children are prone to catching the infection of polio. If every child in the world is vaccinated against polio, the virus of polio will be naturally eradicated as has been done in case of small pox. Therefore, bivalent oral polio vaccine has been given twice a year to all children below the age of five. The programme has made India polio free in 2012. It will, however, continue for some time in four states.

Question 23.
What are vectors ? Name the vectors of malaria and kala- azar. (CCE 2011)
Answer:
Vectors are living organisms which spread the pathogens from infected persons to healthy persons.
Vector of Malaria. Female Anopheles (mosquito).
Vector of Kala-azar. Phlebotomus (Blood sucking Sandfly)

Question 24.
(a) What are communicable diseases ?
(b) What are the common methods of transmission of disease ? (CCE 2011, 2012)
Answer:
(a) Communicable diseases are those diseases which can spread from an infected person to healthy person. They are usually infectious diseases,
(b) Methods of Transmission.

1. Direct or physical,
2. Contact with soil.
3. Animal bites,
4. Transplacental transmission,
5. Air.
6. Water.
7. Contaminated food,
8. Vectors,
9. Fomites.

Question 25.
(a) Why a person suffering from AIDS cannot fight even very small infections ?
(b) In slum area many people are suffering from malaria. Mention any two unhygienic conditions that must be prevailing in that locality.
(c) Why female Anopheles mosquito feeds on human blood ? (CCE 2011)
Answer:
(a) By decreasing the number of T-lymphocytes, HIV weakens the body’s immune system so that even minor infections like common cold become serious diseases like pneumonia.
(b)

1. Stagnant water that becomes breeding place for mosquitoes.
2. Littering of garbage.

(c) Female Anopheles requires proteins from human blood for maturation of its eggs.

Question 26.
(a) List two causes of spread of typhoid.
(b) Mention two ways by which we can prevent the spread of this disease. (CCE 2011)
Answer:
(a) Spread of Typhoid,

1. Contaminated food and water
2. Houseflies.

(b)

1. Underground disposal of human faeces.
2. Disinfection of water and proper cooking of food.

Question 27.
(a) Mohan suffered from chicken pox in his childhood. He would not suffer from this disease again. Mention reason for this.
(b) On which factor the severity of disease manifestation depends ? Explain with an example. (CCE 2011, 2012)
Answer:
(a) One time infection of chicken pox gives a life long immunity against the disease due to development of long- lived memory cells for the same.
(b) Number of microbes above the infective dose and
decreased immunity. A class fellow of yours suffering from common cold is sitting by the side of a few students. Some will catch the disease while the others will not have the same.

Question 28.
(a) Giving any four reasons, justify that it is difficult to prepare antiviral medicines than antibiotics.
(b) Name two diseases caused by viruses.
(c) Name the target organ of malaria.
(CCE 2011, 2012, 2013)
Answer:
(a)

1. Virus does not have its own metabolic machinery. It uses the metabolic pathways of the host,
2. Viruses are highly mutable.
3. Viruses do not live independently. They live and multiply in living cells.
4. Viruses cannot be cultured on artificial medium.

(b) Polio, AIDS,
(c) Liver, RBCs.

Question 29.
Answer the following questions :
(a) Write the expanded from of AIDS.
(b) Name the pathogen of this disease.
(c) List any two modes by which this disease is transmitted. (CCE 2011, 2012, 2013)
Answer:
(a) AIDS. Acquired Immune-Deficiency Syndrome.
(b) HIV or Human Immunedeficiency virus.
(c)

1. Unprotected sexual contact with an infected person,
2. Common needles and syringes.
3. Transfusion of infected blood.
4. Transplacental transmission.

Question 30.
A person was bitten by a stray dog. After some days be becomes irritated. He started fearing water.
(a) Name the disease,
(b) Is there any vaccine available.
(c) Is there any plan of your locality for control of this disease. (CCE 2011)
Answer:
(a) Hydrophobia/rabies
(b) Antirabies vaccine is available but is effective only when it is taken in doses soon after biting of a rabid dog.
(c) No, But all stray dogs as well as pet dogs must be compulsory vaccinated against the disease.

Question 31.
Categorise the following into
acute/chronic/infectious/non- infectious diseases : Typhoid, TB, Goitre, Elephantiasis.
(CCE 2011)
Answer:
Typhoid— Infectious, Acute.
TB— Infectious, chronic.
Goitre— Non-infectious, chronic.
Elephantiasis— Infectious, chronic.

Question 32.
Give cause and remedy of
(a) Hepatits
(b) AIDS
(c) Malaria. (CCE 2011)
Answer:
(a) Hepatitis (Jaundice). Hepatitis virus (A, B, C, D, E or G). Self limited by body defences. Interferon, proper rest and carbohydrate rich food.
(b) AIDS. HIV. ART or antiretroviral treatment.
(c) Malaria. Plasmodium (protozoan). Quinine and its derivatives.

Question 33.
“In our country, majority of children are already immune to hepatitis A without giving its vaccine to them.” Justify this statement giving three reasons. (CCE 2011, 2012)
Answer:

1. Hepatitis A spreads through contaminated water.
2. Poor hygienic conditions prevail in many areas of country. Moreover, young children cannot differentiate between hygienic and non-hygienic conditions.
3. Hepatitis A is one time infection that provides immunity for rest of life.

Question 34.
(a) Ajit is suffering from malaria. Which part of his body will be affected ?
(b) Name the vector for this disease.
(c) Write any one way to prevent the disease. (CCE 2011)
Answer:
(a) Liver followed by RBCs.
(b) Female Anopheles (mosquito)
(c)

1. Using mosquito net while sleeping.
2. Not allowing stagnant water to collect near your residence.

Question 35.
(a) Name the organisms causing the following diseases :

1. Kala-azar
2. (ii) Sleeping sickness.

(b) Given one example each of acute and chronic disease.
(CCE 2011)
Answer:
(a)

1. Kala-azar. Leishmania donovani
2. Sleeping sickness. Trypanosoma gambiense.

(b)

1. Acute Disease: Typhoid,
2. Chronic Disease: Tuberculosis.

Question 36.
What are antibiotics ? How do they work ?
(CCE 2011)
Answer:
Antibiotics are drugs obtained from microbes or prepared synthetically that kill or prevent the growth of pathogenic microbes without harming hosts/human beings. They do so by blocking the biochemical life process of the microbes, without harming human cells, e.g., penicillin prevents cel! wall synthesis while human cells are without cells walls.

Question 37.
(a) Immune system is essential for our health. Comment on the statement.
(b) How can we acquire immunity ? (CCE 2011 )
Answer:
(a) Exemplar Problem 15.
(b) Acquiring immunity is the strengthening of body’s immune system against particular pathogens through stimulating or acquiring the antibodies for their elimination. A previous infection (e.g., Chicken Pox) or vaccination provides active immunity. Antiserum (e.g., antivenin against snake bite) provides passive immunity.

Question 38.
It is diagnosed that Seema suffers from Malaria. Which organ of Seema is affected ?
(a) Which microbe is responsible for this disease ?
(b) What is the symptom of this disease ? (CCE 2011)
Answer:
Organ Affected. Liver followed by RBCs and spleen.
(a) Plasmodium. A protozoan
(b) Symptoms. Malaria attack of 6-10 hours duration is preceded by headache, nausea and muscular pain. Malaria attack begins with chill and shivering (cold stage) followed by high fever (upto 106° F, hot stage) and perspiration (sweating stage).

Question 39.
How do diseases spread through air ? Name two such diseases. (CCE 2011, 2012)
Answer:
Pathogens spread through air over dust and as droplets (emitted by sneezing, coughing and spitting of an infected person). Any body standing or sitting close to the patient will directly inhale these droplets, dust particles and air carrying the infectious agent. Common Cold, Pneumonia.

Question 40.
What is immunisation ? Name any four diseases which can be prevented by immunisation.
(CCE 2011, 2012, 2013)
Answer:
Immunisation is the process of developing immunity against infectious diseases generally through the agency of vaccination.
Four Diseases that can be prevented through immunisation. Diphtheria, Pertussis (Whooping Cough). Tetanus, Influenza type B, Tuberculosis, Measles.

Question 41.
Differentiate between
(a) Acute and chronic diseases
(b) Congenital and acquired diseases
(c) Infectious and non-infectious diseases. (CCE 2011)
Answer:
(a) Acute disease is of shorter duration which does not cause much harm to the body and from which the patient recovers completely without any loss of weight or feeling of weakness. Chronic disease is of longer duration which does harm the affected organ and from which recovery is seldom complete as there is loss of weight and feeling of tiredness.
(b) Congenital disease is the one which is present since birth due to defective development of body (e.g, harelip) or defective heredity (e.g., haemophilia). Acquired disease is the one which develops after birth either due to infection (e.g, malaria) or defective metabolic activity (e.g., hypertension).
(c) Infectious (Communicable) Diseases: These diseases are caused by microbes and other pathogens such as bacteria, viruses, fungi, protozoans, worms, etc. They are called infectious or communicable diseases because the pathogens or infectious agents can spread from diseased person to healthy person by means of air (droplet method), water, food, insects, physical contact, etc., g., tuberculosis, malaria, diarrhoea, etc.
Non-infectious (Non-communicable) Diseases: They are diseases which are not caused by any pathogen or living organism. They are mostly due to internal or intrinsic non-infectious causes. High blood pressure is often caused by excessive weight and lack of exercise.

Question 42.
In a slum area, many people are reported to be suffering from malaria. Mention the unhygienic conditions that must be prevailing there. Name the causative organism. List various preventive measures. (CCE 2011)
Answer:
Unhygienic Condition. Littering of garbage, collection of stagnant water in small and large pits.
Causative Organism. Plasmodium (a protozoan). Preventive Measures,

1. Filling of pits containing stagnant water,
2. Gauze wire on doors and windows.
3. Spray of insecticides in the locality,
4. Use of mosquito net or mosquito repellent,
5. Prophylactic use of antimalarial drugs. Observe the example and complete the rest :

Question 43.
Diabetes : Non-communicable : : Chicken Pox : Communicable.
(a) Malaria : Acute : : Tuberculosis :
(b) Anthrax : Bacteria : : Elephantiasis :
(c) AIDS : Encephalitis : Brain. (CCE 2011)
Answer:
(a) Chronic
(b) Worm (Filaria)
(c) Lymph nodes.

Question 44.
Define immunity. Explain natural and acquired immunity.
Answer:
Immunity is the resistance of the body to a microbial infection even when the microbe is present in infective dose. Immunity is of two types, natural and acquired. Natural Immunity (Innate Immunity). It is a non-specific immunity which either does not allow the pathogen to enter the body (due to physical barriers) or immobilise it with the help of chemicals in body secretions and kill the same by means of phagocytes and other cells. Acquired Immunity. It is specific immunity which develops during the life time of an individual against specific pathogens either due to their infection or by vaccination. In both the cases the body develops antibodies and lymphocytes specific to the pathogens (antigens).

Question 45.
(a) Who discovered vaccine for the first time ?
(b)

1. Name two viral diseases which can be prevented by using vaccines,
2. What is immunity (CCE 2011)

Answer:
(a) Dr Edward Jenner (1876). Vaccine against small pox.
(b)

1. Influenza-B, Polio,
2. Immunity is the resistance of the body to a microbial infection even when the microbe is present in infective dose. Immunity is of two types, natural and acquired. Natural Immunity (Innate Immunity).

Question 46.
Write the cause, symptoms and prevention of AIDS.
(CCE 2011)
Answer:
Cause. Infection of HIV or human immunodeficiency virus. Symptoms,

1. Swollen lymph nodes,
2. Low grade fever with cough, nausea and repeated diarrhoea.
3. Skin rashes developing into ulcers,
4. Sweating at night and weight loss (hence slim disease),
5. Brain damage causing loss of memory, ability to speak and think.
6. Opportunistic infections (due to damage to immune system).

Prevention:

1. Prevention of Overcrowding. Overcrowding leads to spread of infection, especially contagious and air borne. Therefore, proper spacing at home, schools and other public places should be ensured.
2. Sanitation. There should be proper garbage disposal, sewage disposal, covering and cleaning of drains and occasional spraying of insecticides. They keep the environment clean. It reduces the chances of vector borne infections.
3. Drinking Water. Drinking water must be free from all types of germs. It should, therefore, be treated to kill every type of microbial contamination.

Question 47.
(a) What are infectious diseases ? Give two examples.
(b) Name two infectious agents. (CCE 2011)
Answer:
(a) Infectious Diseases. They are diseases that develop in response to attack by pathogens. Infectious diseases are also communicable, i.e., capable of passing from one individual to another, e.g., Malaria, Typhoid, AIDS.
(b) Infectious Agents. Bacteria (e.g., typhoid, cholera), viruses (e.g, AIDS, Chicken Pox, Polio).

Question 48.
Same drug does not work against the microbes belonging to different groups. Why ? State the mechanism of antibiotics in killing bacteria. (CCE 2012)
Answer:
Drugs are used to kill pathogens by blocking their metabolic pathways. Different groups of pathogens have different metabolic systems. Therefore, different sets of medicines are used for treating different types of diseases, e.g., bacterial, fungal, viral, protozoan, helmintic.
Antibiotic kill bacteria by inhibiting their wall synthesis (e.g., penicillin), ribosome functions (e.g., erythromycin, streptomycin) or DNA replication (e.g., ciprofloxacin).

Question 49.
List the names of three diseases caused by virus stating their mode of communication in each case. (CCE 2012)
Answer:

1. Dengue – Aedes mosquito.
2. Influenza-Droplets (air).
3. AIDS-Sexual and blood contact.

Question 50.
(a) For most microbes the organ they target is related to their portal of entry. Furnish details of your answer under the following headings.

(b) Pick up chronic diseases from the list : Japanese encephalitis, Viral fever, Common cold, Tuberculosis.
(CCE 2012)
Answer:
(a)

1. Digestive tract, typhoid
2. Liver, jaundice/hepatitis.

(b) Japanese encephalitis, Tuberculosis.

Question 51.
(a) Which of these is an acute ailment and why ? Tuberculosis, Cancer, Diarrhoea, Elephantiasis.
(b) State two internal, non-infectious causes of disease.
(c) Name the organ that is targeted by the virus which
causes jaundice. (CCE 2012)
Answer:
(a) Diarrhea is an acute ailment which is of shorter duration and does not cuase much harm to the body.
(b) Hypertension, Diabetes,
(c) Liver.

Question 52.
The general way of preventing infections mostly relate to preventing exposure to the disease agent. Explain the statement with three examples. (CCE 2012, 2016)
Answer:

1. Air Borne Microbes. Overcrowding causes rapid spread of air borne and contagious diseases, e.g, common cold. Therefore, proper spacing should be ensured at home, schools and public places.
2. Water Borne Microbes. Safe drinking and bathing water ensures protection against water borne diseases like cholera.
3. (Hi) Vector Borne Microbes. Protection from vector borne microbes (e.g., dengue, malaria) can be obtained by proper garbage disposal, sewage disposal, covering and cleaning of drains and occasional spraying of insecticides.

Question 53.
(a) Why taking an antibiotic is not effective in common cold ?
(b) Name two diseases against which infants below one year are vaccinated.
(c) List two symptoms of any one of these diseases.
(CCE 2012)
Answer:
(a) Antibiotics (e.g, penicillin) are not effective in common cold because common cold is mostly a viral infection while antibiotics are useful in treating only bacterial infections.
(b) Diphtheria, pertussis, tetanus (DPT).
(c) Symptoms of Pertussis

1. Inspiratory whoop
2. Cough.

Question 54.
State the method of transmission of each of the following diseases :

1. Cholera
2. Malaria
3. Pneumonia. (CCE 2012)

Answer:

1. Cholera: Contaminated food and water.
2. Malaria: Female Anopheles.
3. Pneumonia: Through droplets

Question 55.
(a) If penicillin is given to a patient suffering from jaundice, it does not have any effect on the infection. Why ?
(b) Name a disease which has been eradicated from the world.
(c) State the principle behind its eradication. (CCE 2012)
Answer:
(a) Penicillin is an antibiotic which is effective only against bacterial pathogens while jaundice is a viral infection.
(b) Small pox
(c) Universal vaccination.

Question 56.
State reason for the following statements :
(a) Children at the time of birth must be given proper vaccination.
(b) A person suffering from diseases like tuberculosis and flu should be advised to avoid close public contact.
(c) Personal hygiene is very essential for good health.
(CCE 2012)
Answer:
(a) Vaccination protects the neonates from microbial infections.
(b) Tuberculosis and flu are air transmitted diseases.
(c) Personal hygiene or cleanliness keeps one free from contaminations.

Question 57.
(a) Explain when a disease is categorised as a communicable disease. Give two examples each of diseases communicated through

1. Air and
2. Water.

(b) Write one point of difference between communicable and non-communicable diseases. (CCE 2012)
Answer:
(a) Communicable diseases are infectious diseases that can pass from a diseased person to a healthy person by means of transfer like physical contact, air, water, food, vector.

1. Air Transmission: Common cold, pneumonia
2. Water Transmission: Cholera, Hepatitis B, diarrhoea.

(b) A communicable disease can pass from a diseased person to a healthy person. A non-communicable disease cannot pass from a patient to a healthy person.

Question 58.
(a) Which among acute and chronic diseases has adverse effect on health of a person ? Explain giving suitable example.
(b) What is inflammation ? Write the symptoms of this in human body. (CCE 2012)
Answer:
(a) Chronic disease. It lasts for a long time and causes damage to the infected organ, e.g., tuberculosis.
(b) Inflammation is swelling of the area of injury or bite. It is caused by accumulation of tissue fluid (for diluting toxins) and rush of various defence systems to the area causing redness, pain and even fever.

Question 59.
(a) Which disease is more harmful, acute or chronic ? Why ?
(b) Why are we advised to take light and nourishing food when we are sick ? (CCE 2013)
Answer:
(a)Chronic disease. It lasts for a long time and causes damage to the infected organ, e.g., tuberculosis.
(b) Light and nourishing food is easily digestible and provides all the nutrients required for good health.

Question 60.
Sara could not attend the school for a week and her mother did not go to office for six months due to different ailments.
Which category of diseases are they suffering from ? Give an example of each of the above categories. (CCE 2014)
Answer:
Sara is suffering from an acute infectious disease. Her mother is suffering from a chronic disease. Acute disease lasts for a shorter duration and does not cause any damaging effect. Example. Malaria. Chronic disease lasts for a long duration and causes damage to the affected organs. Example. Tuberculosis.

Question 61.
According to a newspaper report, some areas in Delhi received grey coloured water in their taps. It was reportedly due to mixing of contents at some points due to leakage in sewer and water supply pipes. Which kind of diseases are likely to spread due to such problems and why ? Give two specific names of diseases that can thus be spread.
(CCE 2014, 2015)
Answer:
Water borne diseases spread due to use of contaminated water. Examples include hepatitis B, diarrhoea and cholera.
Differentiate between acute and chronic diseases.

Question 62.
Classify the following diseases into two : elephantiasis, dysentery, measles, tuberculosis. (CCE 2014)
Answer:
Acute disease is of shorter duration which does not cause much harm to the body and from which the patient recovers completely without any loss of weight or feeling of weakness. Chronic disease is of longer duration which does harm the affected organ and from which recovery is seldom complete as there is loss of weight and feeling of tiredness.
Congenital disease is the one which is present since birth due to defective development of body (e.g, harelip) or defective heredity (e.g., haemophilia). Acquired disease is the one which develops after birth either due to infection (e.g, malaria) or defective metabolic activity (e.g., hypertension).
Elephantiasis : Chronic disease. Dysentery. Acute disease.
Measles. Acute disease. Tuberculosis. Chronic diseases.

Question 63.
With diagram only depict the common methods of trans¬mission of diseases. (CCE 2014)
Answer:

Ranjan was suffering from severe cold and cough. Still he decided to appear in unit test. Sebhan seated next to Ranjan was not affected but Robin seated behind got infected and suffered a lot. The teacher advised Ranjan to use clean hand¬kerchief during coughing and sneezing.

Question 64.
Answer the folowing questions :

1. Why did Sebhan not got infected ?
2. Which type of disease is cold and cough ?
3. What values are shown by the teacher ? (CCE 2014)

Answer:

1. Sebhan did not get infection due to either having received the pathogen in subinfective dose or possesses higher immunity.
2. Cold and cough is an acute disease.
3. By asking Ranjan to put a clean handkerchief during coughing and sneezing, the teacher has shown his responsibility as a counselor and guide to the student. Use of hand¬kerchief will prevent the spread of infection to other students.

Question 65.
An infant was taken to a doctor for vaccination and a card of the schedule of immunisation was issued to him. Why is he being vaccinated ? Name any three diseases for which he would be vaccinated. (CCE 2015)
Answer:
Vaccination is a method of developing immunisation against some common microbes. An infant is first of all vaccinated with DPT-Hib combined vaccine. It will protect the infant against diphtheria, pertussis (whooping cough), tetanus and influenza type B.

Question 66.
Differentiate between communicable and non-communicable disease in two points. Give one example of each.
(CCE 2015)
Answer:

Question 67.
(a) For the prevention of infectious diseases, some public health programs of childhood immunisation are conducted j in the country. Name four such diseases which are covered under this programme.
(b) Name a disease which has been eradicated from the world. State the principle behind this eradication. (CCE 2015)
Answer:
(a) General Ways of Preventing Infection:
There are two types of general ways of preventing infection, public health measures and personal health measures.

1. Public Health Measures
2. Personal Health Measures.

(b) Small pox

Question 68.
Classify the following diseases as infectious or non-infectious and also mention the cause of non-infectious disease.

1. AIDS
2. Cholera
3. Tuberculosis
4. Pneumonia
5. Colour blindness
6. Diabetes. (CCE 2015)

Answer:

1. AIDS: Infectious,
2. Cholera: Infectious,
3. Tuberculosis: Infectious,
4. Pneumonia: Infectious,
5. Colour blindness: Non-infectious, defective heredity.
6. Diabetes: Non-infectious, hormonal (deficiency of insulin).

Question 69.
Construct a table showing category of agents and one disease / infection caused by each. Why is categorisation required ?
(CCE 2015)
Answer:

1. Virus: HIV, Polio
2. Fungus: Ringworm, Athletes foot.
3. Bacteria: Cholera, T.B.
4. Protozoa: Malaria, Sleeping sickness.
5. Wnm: Ascariasis, Filariasis.

Categorisation of infection causing agents is important as it helps in quicker searching of drugs against them. For ex¬ample, bacterial infections can be treated with the help of antibiotics. In each category, the metabolic pathways of the pathogens will be nearly same. Drugs distrupt these meta¬bolic pathways and kill the pathogens.

Question 70.
A baby is suffering from loose motions. Which factors may be responsible for his condition ? (CCE 2015, 2016)
Answer:
Loose motions or diarrhoea is caused by viral (e.g. Rotavirus) or bacterial (e.g. Salmonella, Shigella) infection. The disease is contracted by contamination of food, milk or water through unhygenic handling by the keeper, soiled utensils or infected care-taker.

Question 71.
Describe in detail the concept of vaccines ? Name four dis¬eases for which vaccines are available in the market ?
(CCE 2015, 2016)
Answer:
Vaccines are preparations containing heat killed or chemically weakened pathogen, or its surface coating which functions as antigens without causing the actual disease. The antigen induces the immune system of the body to develop specific T-lymphocytes and B – lymphocytes against it.
Certain T-lymphocytes function as memory cells. They are long lived. Whenever, the actual pathogen enters the body of immunised person, the memory T-lymphocytes quickly induce the formation of T-lymphocytes and B-lymphocytes to immobilize the pathogen and help in its elimination.
A combined vaccine given to infants against four diseases is DPT-Hib against diphtheria, pertussis, tetanus and Influ- enza-B.

Question 72.
Given below are two situations :

1. Geeta of class IX was having common cold. She sits with Sarika who also develops the disease
2. Animesh of class IX shifted to a new residence with his family where water purification system has not been installed yet. He develops cholera and dysentery. Associate these situations with their mode of transmission and assign appropriate category to them. (CCE 2015)

Answer:

1. Common cold is infectious disease which spreads through droplet method. Sarika must have inhaled the infectious drop-lets and developed the disease.
2. Cholera and dysentery are water (and food) borne diseases which developed in Animesh due to impure contaminated water.

Question 73.
Explain the process of inflammation. Mention the local ef¬fects and general effects of inflammation. (CCE 2015)
Answer:
Inflammation: It is swelling in the region of injury or infection where certain cells are damaged. The damaged cells release histamine which causes dilation of capillaries
and small blood vessels around the area of injury. Many white blood corpuscles come out of the capillaries to kill the pathogens. Cells and antibodies of immune system also become active. The inflammed area becomes painful and red.
Local Effects. The inflammed area becomes red and painful. General Effects. Fever, weakness.

Question 74.
How can you justify the statement ‘prevention of diseases is better than cure’ ? (CCE 2015)
Answer:

Prevention is always better than cure as a disease always causes some damage to the body, loss of working days, besides expenditure on medication. The important precautions for preventing diseases are

1. Hygienic environment
2. Personal hygiene
3. Proper nutrition
4. Clean food
5. Clean water
6. Regular exercise and
7. Relaxation: Every body should also be aware of diseases and their spread. A regular medical check up is also reQuired.
8. Immunisation programme should be followed.

Question 75.
Tabulate three differences between acute and chronic dis¬eases. (CCE 2015)
Answer:

Question 76.
State giving reasons whether the following statements are correct or not

1. Our surrounding area should be free from stagnant water,
2. Staying clean is not necessary as long as you eat a balanced diet,
3. Social equality and harmony are necessary for good health.

Answer:

1. Yes, stagnant water becomes breeding place for mosquitoes which are vectors for many diseases (e.g. Malaria, Dengue, Encephalitis).
2. No, both the aspects, staying clean and balanced diet are important for remaining healthy. Only balanced food will not be sufficient to protect the individual if personal hygiene is lacking.
3. Yes, Social Harmony and Economic Conditions. Social equality, harmony or good relations with neighbours and others in the society are important in sharing joys and sorrows with others, receiving and giving help at the time of need. This gives a sense of belonging that is required for mental health of an individual.

Question 77.
Give the infectious agents in the case of the following diseases :
(a) Kala-azar,
(b) Dengue
(c) Sleeping Sickness. (CCE2015)
Answer:
(a) Kala-azar. Leishmania donovani, a protozoan.
(b) Dengue. DEN, a virus
(c) Sleeping Sickness. Trypanosoma gambiense.

Question 78.
Classify the following diseases as infectious and non-infec¬tions : AIDS, Tuberculosis, Cholera, High blood pressure, Pneumonia, Cancer. (CCE 2016)
Answer:
Infectious. AIDS, Tuberculosis, Cholera, Pneumonia. Non-infectious. High blood pressure, Cancer.

Question 79.
From where does the term disease originate ? ( CCE 2016)
Answer:
(a) The word disease originated from dis without and ease comfort or discomfort in the functioning of the body or its part.

Question 80.
(a) Antibiotics are successful in curing bacterial infections
but do not cure viral infections. Why ?
(b) Which system of the body is activated in response to infection and how it responds ?
(c) Name any two organisms from which antibiotics are extracted. ( CCE 2016)
Answer:
(a) Antibiotics are effective against bacterial infections because they disrupt the metabolic machinery of bacteria. Viruses do not have their own metabolic machinery. Therefore, antibiotics are unable to control viral infections.
(b) The body system activated in response to an infection is immune system. It responds to an infection by producing T-lymphocytes and B-lymphocytes that immobilise and kill the pathogen.
(c) Antibiotic Producing Organis. Pénicillium, Streptomyces.

Question 81.
Raju of class DC was suffering from chicken pox. His friends Priya and Shaurya wanted to visit him. Shaurya’s parents did not allow him to go. Priya had already suffered from chicken pox a few months before. Priya parents allowed her to visit him. What could be the reason behind their parents’ decision ? (CCE 2016, 2017)
Answer:
Chicken pox is an infectious/contagious disease. Shaurya’s parents did not allow him to visit Raju because he could catch chicken pox form him. Priya’s parents allowed her as she had developed immunity against the disease after suffering from it a few months ago. This immunity perists for life. Basis of Immunisation. Developent of pathogen specific T-lymphocytes and B-lymphocytes so as to kill the same if it enters the body. This is done through administration of antigen or immobilised pathogen. Duration of immunity depends upon the memory cells.

Question 82.
Explain any three means by which infectious diseases are spread. ( CCE 2016)
Answer:
By sexual and blood contact in case of AIDS, syphilis and some other diseases.
By vectors and carriers, e.g., malaria by female Anopheles.

Question 83.
(a) Differentiate between acute and chronic diseases (give two points).
(b) Give one example each of acute and chronic disease.
(CCE 2016)
Answer:

Question 84.
(a) What are antibiotics ?
(b) Penicillin is not effective against common cold. Justify the statement by giving appropriate reason. (CCE 2016)
Answer:
(a) Antibiotics are drugs obtained from microbes or prepared synthetically that kill or prevent the growth of pathogenic microbes without harming hosts/human beings. They do so by blocking the biochemical life process of the microbes, without harming human cells, e.g., penicillin prevents cell wall synthesis while human cells are without cells walls.
(b) Diphtheria, pertussis, tetanus (DPT).

Question 85.
(a) What is immunisation ? How does it help people ?
(b) List two diseases for which vaccines are provided under Public Health Programme. ( CCE 2017)
Answer:
(a) Immunisation is the process of developing immunity against infectious diseases generally through the agency of vaccination.
Immunisaton protects people from the disease against which vaccination has been provided.
(b) Four Diseases that can be prevented through immunisation. Diphtheria, Pertussis (Whooping Cough). Tetanus, Influenza type B, Tuberculosis, Measles.

Question 86.
Mention any three factors necessary for a person to live healthy life. (CCE 2017)
Answer:

1. Environment
   1. A clean physical environment with the help of public health services,
   2. A congenial social environment.
2. Personal Hygiene: Personal cleanliness prevents catching up of infectious diseases.
3. Nourishment: A proper balanced diet keeps the immune system strong.
4. Vaccination: Timely vaccination against major diseases protects oneself from catching those diseases.
5. Avoiding overcrowded areas
6. Regular exercise and relaxation.

Question 87.
Which part of the body is attacked by the bacteria causing I tuberculosis if they enter through
(a) Nose
(b) Mouth.
(CCE 2017)
Answer:
(a) Through Nose: Pulmonary tuberculosis,
(b) Through Mouth: Intestinal tuberculosis,

Question 88.
Differntiate between infectious and non-infeclious diseases (any three differences). ( CCE 2017)
Answer:

Long Answer Questions

Question 1.
(a) Write two differences between communicable and non communical diseases,
(b) Mention any three methods that can cause spreading of AIDS. (CCE 2013)
Answer:
(a)

(b) Methods of Spreading AIDS:

1. Unprotected sexual contact with an infected person,
2. Common needles and syringes.
3. Transfusion of infected blood.
4. Transplacental transmission.

Question 2.
(a) What do you mean by inflammation ? What are its common effects ?
(b) Name the organ affected in a patient showing the symptoms of persistent cough and breathlessness,
(c) Which group of microbes cause diseases like malaria and kala-azar ? (CCE 2013)
Answer:
(a) Inflammation: It is swelling in the region of injury or infection where certain cells are damaged. The damaged cells release histamine which causes dilation of capillaries
and small blood vessels around the area of injury. Many white blood corpuscles come out of the capillaries to kill the pathogens. Cells and antibodies of immune system also become active. The inflammed area becomes painful and red.
(b) Lung,
(c) Protozoans (Plasmodium in malaria and Leishmania in kala-azar).

Question 3.
List the following diseases into communicable and noncommunicable diseases :

1. Cancer
2. High blood pressure
3. Common cold
4. Diabetes
5. Tuberculosis
6. Night blindness
7. SARS
8. Typhoid
9. Cholera
10. Dengue. (CCE 2014)

Answer:

1. Cancer: Noncommunicable.
2. High Blood Pressure: Noncommunicable.
3. Common Cold: Communicable.
4. Diabetes: Noncommunicable.
5. Tuberculosis: Communicable,
6. Night Blindness: Noncommunicable.
7. SARS: Communicable,
8. Typhoid: Communicable,
9. Cholera: Communicable,
10. Dengue: Communicable.

Question 4.
Mr. Iyer had cold and throat infection. Doctor prescribed an antibiotic,
(a) Which pathogens could have caused the infection ?
(b) What is the mode of action of antibiotics ? Mr. Iyer recovered from cold but he still had throat infection. Would the doctor continue the antibiotic further ? State yes or no giving reason . (CCE 2014)
Answer:
(a) Cold is commonly caused by virus while soar throat can be due to bacterial infection or allergy.
(b) Antibiotics act on bacteria and kill them by inhibiting their metabolic reactions (e.g., cell wall formation , ribosome functioning ).
Since soar throat continues, the doctor can continue to prescribe antibiotic for 3-4 days because bacterial soar throat takes about 10 days to heal.
A person is suffering from breathlessness, loss of body weight, persistent cough, feels tired and produces blood stained sputum.

Question 5.
(a) Name the type/category of disease based on duration.
(b) Name the disease and its causative agent
(c) How this disease is transmitted ?
(d) Which body part is attacked by the causative agent/pathogen ? (CCE 2014)
Answer:
(a) Chronic disease.
(b) Tuberculosis, Mycobacterium tuberculosis,
(c) Through droplet method and sputum (infected ).
(d) Lung.

Question 6.
(a) What do signs and symptoms indicate if a person is suffering from any disease ?
(b) Based on the duration of disease, what are the different
categories of diseases ? Differentiate between them with one example each. (CCE 2014)
Answer:
(a) Symptoms indicate presence of disease due to structural and functional changes in the body due to it, e.g., fever, loose motion. Signs are definite indications of particular diseases based on symptoms, e.g., intermittent fever in malaria. The same are confirmed by tests.
(b) Based on duration, diseases are of two types, acute and chronic.
Acute disease is of shorter duration which does not cause much harm to the body and from which the patient recovers completely without any loss of weight or feeling of weakness. Chronic disease is of longer duration which does harm the affected organ and from which recovery is seldom complete as there is loss of weight and feeling of tiredness.

Question 7.
(a) Identify the organism shown in the picture and write the common name and scientific name of the organism.

(b) Name the phylum and kingdom.
(c) Which organ of digestive system normally harbours this organism ?
(CCE 2014)
Answer:
(a) Common Roundworm, Ascaris lumbricoides
(b) Nemathelminthes (Phylum), animalia (kingdom),
(c) Intestine.

Question 8.
Health is not merely absence of diseases. How can we define health ? Classify diseases on the basis of
(i) Duration of diseases
(ii) Cause of diseases. Give one example of each type.
(CCE 2014, 2016)
Answer:
DefinitionDisease: It is a condition of the body or a part of it in which functions are disturbed or damaged.(i) Classification Based on Duration of Disease.
(i) Acute disease is of shorter duration which does not cause much harm to the body and from which the patient recovers completely without any loss of weight or feeling of weakness. Chronic disease is of longer duration which does harm the affected organ and from which recovery is seldom complete as there is loss of weight and feeling of tiredness.
(ii) Classification Based on Cause of Disease:

1. Pathogens. Many bacteria, viruses, fungi, protozoans and worms produce diseases, spreading from an infected
   person to healthy one through various means of transport, e.g., Malaria, Diarrhoea, TB.
2. Deficiency. Nutrient deficiency including that of minerals and vitamins, leads to several diseases like marasmas, kwashiorkor, pellagra, goitre, anaemia.
3. Genetic Disorders. Caused by defective heredity, e.g., haemophilia.
4. Degenerative Disorders. Natural defects appearing due to senescence, e.g., hypertension, atherosclerosis, arthritis.

Question 9.
State four differences between infectious and noninfectious diseases giving one example of each. (CCE 2014)
Answer:

Mrs. Chaturvedi had just recovered from tuberculosis. She still felt weak and tired all the time.

Question 10.
What do you infer about the type of disease ? Write three characteristics of such diseases. Name two other diseases belonging to this category. (CCE 2015)
Answer:
Tuberculosis is a chronic disease of lungs. Despite her recovery, Mrs. Chaturvedi is unable to obtain required oxygen and hence energy due to permanent damage to lungs and some other parts of the body.
Characteristics of Chronic Diseases:

1. Duration: Chronic diseases are long duration diseases,
2. Build up: The disease begins with milder course but builds up with time.
3. Fatigue: The patient feels tired with shortness of breath, poor appetite and loss of weight.
   Other Examples. Diabetes, Hypertension.

Question 11.
“Over crowded and poorly ventilated housing is a major factor in the spread of air-borne diseases. Explain the statement and support vour answer with diagram also.
(CCE 2015, 2016)
Answer:
Air borne diseases are mostly the ones which infect nose, throat and lungs (cold, flu, pneumonia, tuberculosis), as they lie in the passage way of breathed air. A patient suffering from such a disease will send out the pathogens in droplets during coughing and sneezing. Any body present with in 2 metre distance of the patient will inhale the same and get inflected. As the liquid in the droplets evaporates, droplet nuclei are formed which continue to circulate and re-circulate in the air. In poorly ventilated and over-crowded accomodation, the droplet nuclei will be inhaled by every body and infect the same.

Question 12.
Give the ways by which microbial agents can commonly move from infectious person to someone else for the following diseases.
(a) Cholera
(b) Pneumonia
(c) Common cold
(d) Malaria
(e) Fungal infection. (CCE 2015)
Answer:
(a) Cholera. Contaminated water and food, directly or through flies.
(b) Pneumonia. Droplet transmission.
(c) Common Cold. Droplet transmission,
(d) Malaria. By female Anopheles (mosquito).
(e) Fungal Infection. Direct or indirect contact.

Question 13.
Justify the statement,
(a) Availability of proper and sufficient food would protect from infectious diseases,
(b) The general ways of preventing infection mostly relate to preventing exposure. List three points of prevention of exposure.
(CCE 2015)
Answer:
(a) Proper and sufficient food means that the person develops a good health so that all body systems function optimally. The immune system becomes strong. A strong immune system protects the body from many infectious diseases if the infective dose is not very large.
(b)

1. Air Borne Microbes. Overcrowding causes rapid spread of air borne and contagious diseases, e.g, common cold. Therefore, proper spacing should be ensured at home, schools and public places.
2. Water Borne Microbes. Safe drinking and bathing water ensures protection against water borne diseases like cholera.
3. Vector Borne Microbes. Protection from vector borne microbes (e.g., dengue, malaria) can be obtained by proper garbage disposal, sewage disposal, covering and cleaning of drains and occasional spraying of insecticides.

Question 14.
Explain giving reasons :
(a) Balanced diet is necessary for maintaining healthy body,
(b) Health of an individual depends upon the surrounding environmental conditions.
(c) Our surrounding areas should be free from stagnant water.
(d) Social harmony and good economic conditions are necessary for good health. (CCE 2015)
Answer:
(a) Proper and sufficient food means that the person develops a good health so that all body systems function optimally. The immune system becomes strong. A strong immune system protects the body from many infectious diseases if the infective dose is not very large.
(b) Environmental Conditions. A clean environment with regular disposal of garbage, drainage and sewage services prevents growth of vectors and pests. Fewer diseases occur in such an area. On the other hand, a filthy environment with poor drainage and sewage services will cause increased number of infections.
(c) Stagnant Water. It is source of mosquito breeding, stink and other unhygenic conditions. It promotes vector borne diseases.
(d) Social Harmony and Economic Conditions. Social equality, harmony or good relations with neighbours and others in the society are important in sharing joys and sorrows with others, receiving and giving help at the time of need. This gives a sense of belonging that is required for mental health of an individual.
Good economic conditions provide proper nutrition, clothing, education, health care, outings and other facilities in the family that are helpful to maintain physical and mental health of all the members.

Question 15.
“Educating parents would help a lot in reducing incidences of diseases in children”. Justify the statement with five reasons. (CCE 2019)
Answer:
Children are dependent upon their parents for their nutrition, hygiene, upkeep and protection from diseases. It is, therefore, important to educate the parents about the same.

1. Balanced Diet: A child should be given proper diet that is balanced, nutritive and having ingredients required for growth.
2. (it) Clean Food and Water: The food and water given to the children should be free from all contaminants. The food should be prepared fresh while water should be properly filtered or preboiled and cooled.
3. Proper Hygiene: Children should have a daily bath, cleaning of teeth, hand washing, clean clothes and taken care while crawling or playing so that they do not catch up any pathogen.
4. Regularity: A child requires a regular routine which should involve proper rest, proper excercise, timing of feeding, bathing, sleeping and recreation.
5. Vaccination: Sticking to vaccination schedule for children is a must for avoiding many diseases.

Question 16.
(a) “An exposure with an infectious microbe does not necessarily mean developing noticeable disease.” Do you agree ? Explain with reason.
(b) If yes, how severe infections occur in our body ?
(CCE 2019
Answer:
(a) An infectious microbe is able to cause a disease only if the immune system of the person is unable to put proper defence against it. Many persons have strong immune system or have acquired immunity against the pathogen or the pathogen attack is less than the infective dose. In such cases, despite exposure to infective microbe, the person will not catch the disease.
(b) Severe Infections. They occur when the immune system of the body has become weak or the person has suffered from a previous infection and is just recovering or the person is suffering from dietary deficiencies, or is surrounded by unhygenic environment.

Question 17.
(a)

1. Why an antibiotic is not effective in the common cold ?
2. Name two diseases against which infants below one year are vaccinated,
3. List two symptoms of any one of these diseases.

(b) The general way of preventing infections mostly relate to peventing exposure to the disease agent. Explain the statement with examples. (CCE 2019)
Answer:
(a)

1. Antibiotics (e.g, penicillin) are not effective in common cold because common cold is mostly a viral infection while antibiotics are useful in treating only bacterial infections.
2. Diphtheria, pertussis, tetanus (DPT).
3. Symptoms of Pertussis
   1. Inspiratory whoop
   2. Cough.

(b)

1. Air Borne Microbes. Overcrowding causes rapid spread of air borne and contagious diseases, e.g, common cold. Therefore, proper spacing should be ensured at home, schools and public places.
2. Water Borne Microbes. Safe drinking and bathing water ensures protection against water borne diseases like cholera.
3. Vector Borne Microbes. Protection from vector borne microbes (e.g., dengue, malaria) can be obtained by proper garbage disposal, sewage disposal, covering and cleaning of drains and occasional spraying of insecticides.

Question 18.
(a) What kind of food is advised when we fall sick and why ?
(b) Mention any three basic conditions required for good health. (CCE 2019)
Answer:
(a) Bland, easily digestible and balanced food that provides all the ingredients for proper functioning and recovery of the body.
(b) Good Health. The three basic conditions required for good health are :

1. Freedom from disease and infirmity.
2. Social well being.
3. Absence of mental problems.

Question 19.
(a) (i) Write the principles of treatment that are generally followed by a doctor to treat infectious diseases.
(ii) Write any two ways by which HIV (AIDS virus) may get transmitted from one person to another.
(b) Antibiotics can control bacterial infections but not viral infections. Why ? (CCE 2019)
Answer:
(a)
(i) There are two ways to treat an infectious disease. They are

1. Reduce the Effect of Disease by
   1. Symptomatic treatment like use of antipyretic, analgesic, antidiarrhoeal or antiallergic medicine,
   2. Bed rest.
2. Killing the Infectious Agent. After proper diagnosis of the pathogen, pathogen specific medicine is given to kill the same. Antibiotic medicines are available for killing bacterial pathogens. Similarly anti-fungal anthelmintic and antiprotozoan medicines are also available. However, very few antiviral medicines are available as viruses do not have any metabolic machinery of their own (which can be attacked by any medicine).

(ii)

1. Unprotected sexual contact with an infected person,
2. Common needles and syringes.
3. Transfusion of infected blood.
4. Transplacental transmission.

(b) Antibiotics are effective against bacterial infections because they disrupt the metabolic machinery of bacteria. Viruses do not have their own metabolic machinery. Therefore, antibiotics are unable to control viral infections. Differentiate between

Question 20.

1. Acute disease and chronic disease
2. Infectious disease and noninfectious disease
3. Symptom based treatment and microbe based treatment
4. Antibiotics and vaccines
5. Congenital disease and acquired disease.
   (CCE 2016)

Answer:

1. Acute and Chronic Disease.
   An acute disease is of shorter duration which causes little damage to the body.
   A chronic disease is of longer duration which damages the body system affected by it.
2. Infectious and Noninfectious Diseases.
   Infectious or Communicable Diseases. The diseases are caused by pathogens like : Bacterial, e.g., typhoid, tuberculosis,
   Non-infectious or Non-communicable Diseases. The diseases are caused by metabolic disorders, hormonal imbalance and degenerative changes, e.g., diabetes, hypertension.
3. Symptoms Based Treatment and Microbe Based Treatment. Symptom based treatment is meant for giving immediate relief to the body from effect of the disease while microbe based treatment is meant for eliminating the disease causing microbe.
4. Antibiotics and Vaccines. Antibiotics are drugs (basically produced by microbes) which are used to eliminate disease causing bacteria. Vaccines are preparations containing heat killed or chemically weakened pathogens or their coating which are used to develop immunity against the disease.
5. Congenital Disease and Acquired Disease.
   Congenital Disease is present from birth, e.g., hare-lip, haemophilia.
   Acquired Disease id the disease is picked up after birth. Acquired diseases are of two types, infectious and non-infectious.

Question 21.

1. (i) List two conditions essential for health,
   (ii) Healthy balanced diet helps in preventing diseases. How ?
2. State in tabular form the method of transmission of each of the following diseases :
   (i) Cholera
   (ii) HIV—AIDS
   (iii) Malaria
   (iv) Pneumonia.
   (CCE 2016)

Answer:

1. (i) Absence of disease, physical, mental and social well being,
   (ii) Proper balanced nourishment maintains the health of all body systems including the immune system.
2. Cholera— Contaminated food and water HIV-AIDS— Sexual contact, Blood contact.
   Malaria — Female Anopheles Pneumonia— Air transmission.

Question 22.

1. Name any one disease caused by each of the following :
   1. Protozoa
   2. Virus
   3. Bacteria
   4. Fungi.
2. How is malaria disease transmitted ?
3. What are the common preventive measures taken against communicable diseases ? (CCE 2017)

Answer:

1. 1. Protozoa. Malaria
   2. Virus. Chicken pox
   3. Bacteria. Typhoid
   4. Fungi. Ringworm.
2. Female Anopheles. While sucking blood from a sick person to healthy person.
   1. Vaccination
   2. Protection from mosquitoes
   3. Protection from contamined food and water
   4. Hygienic living.

Question 23.
Associate the following diseases/infections with their causative agents :

1. Sleeping sickness
2. SARS
3. Kala- azar
4. Acne
5. AIDS
6. Dengue fever
7. Malaria
8. Brain fever
9. Chicken pox
10. Polio. (CCE 2017)

Answer:

1. Sleeping Sickness. Trypanosoma gambiense (a protozoan)
2. SARS (Severe Acute Respiratory syndrome). Virus, SARS-coV.
3. Kala-azar. Leishmania donovani ( a protozoan).
4. Acne. Staphylococus (a bactrium).
5. AIDS. HIV (Human Immuno deficiency Virus)
6. Dengue Fever. Virus (DENV).
7. Malaria. Plasmodium (a protozoan).
8. Brain Fever. Virus (Flavi Virus)
9. Chicken pox. Virus (Varicella zoster)
10. Polio. Polio Virus.

Hope given Previous Year Question Papers for CBSE Class 9 Science Chapter 13 Why Do we Fall Ill are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 16 Floatation Class 9 Science Important Questions with Answers PDF will help you in scoring more marks in your exams.

Floatation Class 9 Important Questions and Answers Science Chapter 16

VERY SHORT ANSWER QUESTIONS

Based on Thrust and Pressure

Question 1.
Define ‘thrust’. (CBSE 2011, 2014, 2016)
Answer:
The total force exerted by a body perpendicular to the surface is known as thrust.

More Resources

• Previous Year Question Papers for CBSE Class 9 Science
• NCERT Solutions for Class 9 Science
• NCERT Exemplar Solutions for Class 9 Science
• Value Based Questions in Science for Class 9
• HOTS Questions for Class 9 Science

Question 2.
What is the unit of thrust in SI ? (CBSE 2013, 2016)
Answer:
S.I. unit of thrust is newton (N).

Question 3.
Define the term ‘pressure’. (CBSE 2011, 2013, 2014, 2016)
Answer:
Pressure is defined as the force acting perpendicular on unit area of the surface.

Question 4.
Name the SI unit of pressure. (CBSE 2013, 2016)
Answer:
S.I. unit of pressure is N/m² or pascal.

Question 5.
State the relationship between thrust and pressure. (CBSE 2010, Term I, 2013, 2014)
Thrust
Answer:

Question 6.
Define 1 pascal. (CBSE 2014, 2015, 2016)
Answer:
1 pascal is defined as the pressure exerted by 1 N force acting perpendicular on the surface of 1 m² area.

Based on Buoyant Force

Question 7.
Define upthrust or buoyant force. (CBSE 2010, 2011, 2012, 2016)
Answer:
The upward force exerted by a liquid on a body which is immersed in the liquid is known as upthrust or buoyant force.

Question 8.
State the factors on which upthrust or buoyant force depends. (CBSE 2010, 2011, 2012, 2016)
Answer:

1. Size or volume of body immersed in a liquid,
2. Density of the liquid in which the body is immersed and
3. Acceleration due to gravity at the given place.

Question 9.
When an object is immersed in a fluid, name the two forces acting on it. (CBSE 2011, 2012, 2016)
Answer:

1. Weight of object in the vertically downward direction,
2. Upthrust or buoyant force in the vertically upward direction.

Question 10.
Name the force experienced by an object in a fluid when immersed in it. What is its direction ?
(CBSE 2011)
Answer:
Upthrust or Buoyant force. It acts on the object in upward direction.

Question 11.
Why does a block of wood held under water rise to the surface when released ? (CBSE 2011)
Answer:
This is because the buoyant force or upthrust acting on the wooden block due to water is greater than the weight of the block.

Question 12.
An object of weight 200 N is floating in a liquid. What is the magnitude of the buoyant force acting on it? (CBSE 2011)
Answer:
Magnitude of buoyant force = 200 N.

Question 13.
Explain the factors which determine whether an object floats or sinks when placed on the surface of water.
(CBSE 2011)
Answer:

1. Volume of the object and
2. density of the water.

Question 14.
Name the force acting on a body, when it is fully or partially immersed in a liquid. (CBSE 2011)
Answer:
Buoyant force.

Question 15.
What will be the direction of buoyant force when suppose the weight of an object is acting from north to south in the fluid ? (CBSE 2013)
Answer:
From south to north as buoyant force acts opposite to the direction of the weight of the object.

Question 16.
A body of weight 20 N floats half submerged in a liquid. What is the buoyant force on the body ?
Answer:
20 N

Based on Archimedes’ Principle

Question 17.
State Archimedes’ principle. (CBSE 2010, 2011, 2012, 2015)
Answer:
When a body is immersed partially or completely in a fluid (liquid or gas), it experiences an upthrust or buoyant force which is equal to the weight of the fluid displaced by the body. The weight of the body decreases due to the buoyant force acting on the body, when immersed in a fluid. In other words, a body loses its weight, when immersed completely or partially in a fluid. The loss of weight of a body in a fluid is equal to the upthrust or buoyant force.
The upthrust or buoyant force = weight of fluid displaced by a body = weight of body in air – weight of body in fluid.

Question 18.
Write the relationship between buoyant force acting on an object and weight of the liquid displaced by it. (CBSE 2010, 2012)
Answer:
Buoyant force = weight of liquid displaced by the object.

Question 19.
State the physical expression relating weight of the body in the liquid, actual weight of the body in air and the weight of the liquid displaced by the body. (CBSE 2011, 2013)
Answer:
Weight of a body in a liquid = actual weight of the body – weight of the liquid displaced by the body.

Question 20.
Give any two examples where Archimedes’ principle is applied . (CBSE 2011, 2012)

                                                  Or

List two applications of Archimedes’ principle. (CBSE 2012, 2016)
Answer:
Archimedes’ principle is applied in designing

1. ships and submarines and
2. lactometer used for testing the purity of milk.

Question 21.
State the principle on which working of hydrometer is based. (CBSE 2011)
Answer:
Archimedes’ principle:
A Greek scientist Archimedes conducted many experiments and concluded that when a body or an object is immersed partially or completely in a liquid or a gas (i.e., fluid), it experiences an upthrust or buoyant force. The upthrust or buoyant force is equal to the weight of the fluid displaced by the body. As a result of the buoyant force acting on an object, the weight of the object decreases, when immersed in a fluid. The finding of Archimedes is known as Archimedes’ principle.
Archimedes’ principle is used to design :

1. the ships and submarines
2. the hydrometers to find the densities of liquids
3. the lactometers to test the purity of milk.

Based on Density and Relative density

Question 22.
Define density. Give SI unit of density. (CBSE 2011, 2012, 2014, 2015)
Answer:
Density of an object is defined as mass per unit volume of the object. That is, density = mass/volume .
S.I. unit of density is kg/m³ (kg m^-3).

Question 23.
Define relative density of a substance. (CBSE 2011, 2012, 2013, 2014, 2015)
Answer:
It is defined as the ratio of the density of the substance to the density of water.

Question 24.
If the relative density of a substance is less than 1, will it float or sink in water ? Support your answer.
(Density of water = 1000 kg/m³). (CBSE 2011)
Answer:

As relative density of substance is less than 1, so density of substance is less than the density of water. Hence, the substance will float in water.

Question 25.
Relative density of aluminium is 2.7. Explain this statement. (Similar CBSE 2011)
Answer:
Aluminium is 2.7 times heavier than the equal volume of water.

Question 26.
The density of a solid is 7.9 g cm^-3 in air. What is the density of the solid in SI unit (kg m^-3) ?
(CBSE 2016)
Answer:
Density = 7.9 g cm^-3 = 7.9 x 1000 kg m^-3 = 7.9 x 10³ kg m^-3.

Question 27.
Relative density of gold is 19.3. The density of water is 1000 kg/m³. What is the density of gold in SI units ? (CBSE 2011, 2013, 2014, 2017)
Answer:
Density of gold = Relative density of gold x density of water = 19.3 x 1000 kg/m³ = 19300 kg/m³

SHORT ANSWER QUESTIONS

Based on thrust and pressure

Question 1.
Differentiate between thrust and pressure. State the unit in which they are measured.
Answer:
Thrust: The total force exerted by a body perpendicular to the surface is known as thrust.
Pressure: Pressure is defined as the force acting perpendicular on unit area of the surface.
S.I. unit of thrust is newton (N).
S.I. unit of pressure is N/m² or pascal.

Question 2.
The wheels of an army tank rest on a steel belt. Give reason.

                                                   Or

Why an army tank weighing more than a thousand tonne rests upon a continuous chain. (CBSE 2012, 2015)
Answer:
Pressure exerted by army tank on the ground is given

Since area of steel belt is more than the area of the wheels of the tank, so tank exerts less force on the ground. Hence, the ground under the tank does not sink under the weight of the tank.

Question 3.
Why are railway tracks laid on large sized concrete sleepers ? Explain. (CBSE 2011)
Answer:
The weight or thrust of the train is spread over large area of sleepers. Therefore, the pressure acting on the
ground under the sleepers is reduced. This prevents the sinking of the ground under the weight of the train.

Question 4.
Why do buildings have wide foundations ?
Answer:
So that the weight of the buiding is spread over a large area and hence less pressure is exerted on the ground. Hence, the building is prevanted to sink under its weight.

Question 5.
Which will exert more pressure, 100 kg mass on 10 m³ or 50 kg mass on 4 m² ? Give reason.
(CBSE 2011, 2014, 2015)
Answer:

Thus, P₁ > P₂.

Question 6.
Explain, why a truck or a motor bus has much wider tyres ? (CBSE 2011, 2015, 2016)
Answer:
The weight of truck or motor bus spreads over large area on the surface of road or ground and hence less pressure is exerted by truck or a motor bus on the road. Therefore, the ground under them does not sink.

Question 7.
Account for the statement : “camel walks easily on sand but it is difficult for a man to walk on sand though a camel is much heavier than a man”. (CBSE 2011)
Answer:
A camel walks easily on the sandy surface than a man inspite of the fact that a camel is much heavier than a man.
This is because the area of camel’s feet is large as compared to the area of man’s feet. So the pressure exerted by camel on the sandy surface is very small as compared to the pressure exerted by man. Due to large pressure, sand under the feet of a man yields (i.e., sink) and hence he cannot walk easily on the sandy surface. On the other hand, sand under the feet of camel does not sink much due to small pressure. Hence camel can walk and run easily on the sandy surface.

Question 8.
A Sharp knife is more effective than a blunt knife. Why ? (CBSE 2012)

                                                 Or

Cutting and piercing tools are made sharp. Give reason. (CBSE 2015)
Answer:
Pressure (P = F/A) exerted by sharp knife on an object is more than the pressure exerted by a blunt knife. Therefore, sharp knife is more effective in cutting the object than a blunt knife.

Question 9.
Why does an iron nail sinks in water but a wooden cork floats on water ? (CBSE 2011, 2012, 2015, 2016)
Answer:
The weight of iron is greater than the upthrust of water on the iron nail, so iron nail sinks in water. On the other hand, the upthrust on cork is more than the weight of the cork. Hence wooden cork floats on water.

Question 10.
A balloon filled with hydrogen gas floats in air. Explain why ?
Answer:
The upthrust or buoyant force acting on hydrogen balloon is greater than the weight of the hydrogen balloon. So it floats in air.

Question 11.
An object of volume V is immersed in a liquid of density p. Calculate the magnitude of buoyant force acting on the object due to liquid.
Answer:
Magnitude of buoyant force acting on the object due to liquid = weight of liquid displaced
= mass of liquid displaced x g (∴ W = mg)
= Volume of body x density of liquid x g = Vρg
Thus, buoyant force depends upon

1. the volume of the immersed portion of the object and
2. density of the liquid.

Question 12.
An object is immersed in different liquids. Is same buoyant force acts on the object due to all liquids ?
(CBSE 2011)
Answer:
We know, buoyant force acting on an object due to a liquid is directly proportional to the density of the liquid. Since different liquids have different densities, so different buoyant forces act on the object due to different liquids. An iron sphere is suspended with an iron string.

Question 13.
The length of the string increases (i.e. string is stretched). Now the iron sphere is completely immersed in water and the increase in length of the string decreases. Explain why? (CBSE 2011)
Answer:
The length of the string increases due to the weight of the suspended iron sphere. When the sphere is immersed in water, buoyant force due to water acts on the sphere in the upward direction.
Now, the net force (or weight) acting on the string = actual weight of the sphere – buoyant force acting on it.
Since the net force acting on the string decreases and hence the extension of the string also decreases.

Question 14.
Two blocks, one of iron and other of wood are immersed in water at the same depth. Will both come upward ? Why ? (CBSE 2011)
Answer:
Wooden block will come upward. This is because upthrust of water on the wooden block is greater than its weight. In other words, density of wood is less than the density of water and density of iron is greater than the density of water.

Question 15.
Lead has greater density than iron and both are denser than water. Is the buoyant force on a lead object greater than or lesser than or equal to the buoyant force on an iron object of the same volume ? Explain your answer giving reason. (CBSE 2011)
Answer:
Buoyant force on an object depends upon

1. the volume of the object and
2. density of the liquid in which the object is immersed.

Since volume of both objects is same and both are immersed in water, therefore, buoyant force on lead object is equal to the buoyant force on iron object.

Question 16.
Explain, why a truck or a motor bus has much wider tyres ? (CBSE 2011, 2015, 2016)
Answer:
The weight of truck or motor bus spreads over large area on the surface of road or ground and hence less
pressure is exerted by truck or a motor bus on the road. Therefore, the ground under them does not sink.

Question 17.
A ship is loaded in sea water to maximum capacity. What will happen if this ship is moved to river water ? Why? (CBSE 2011)
Answer:
When ship is moved to river water from sea water, then upthrust acting on the ship decreases because density of river water is less than the density of sea water. Hence, the net weight of the ship will be more in river water than in sea water. Hence, more portion of the ship will be inside the river water.

Question 18.
Why do we feel lighter when we swim ?

                                        Or

When we jump into a swimming pool, we feel lighter. Why ? (CBSE 2011)
Answer:
When we swim in water, two forces acts on our body. One is the gravitational force equal to our weight in the downward direction and the other is the up thrust or buoyant force in the upward direction. Hence, the net downward force or the apparent weight of our body is less than our actual weight. Therefore, we feel lighter, when we swim.

Question 19.
An egg sinks in fresh water but floats in highly salty water. Give reason. (CBSE 2012)
Answer:
Upthrust acting on egg in fresh water is less than the weight of egg. Therefore, it sinks in fresh water. However,
the density of salty water is much greater than the density of fresh water, so upthrust acting on egg in salty water is greater than the weight of egg. Therefore, it floats in salty water.

Question 20.
The following figure shows three identical blocks of wood floating in three different liquids A, B and C of densities d₁, d₂ and d₃ respectively. Which of these has the highest density. Give reason to justify your answer.
(CBSE 2012)

Answer:
In case of liquid C, upthrust is maximum. Since upthrust depends on the density of liquid, therefore, density of liquid C (i.e., is the highest.

Question 21.
When an object is immersed into the fluid, two forces act on the object in the vertically opposite directions. Name them and also write the factors on which the magnitude of these forces depends on. (CBSE 2012, 2015)
Answer:

1. Weight of object = mg. It depends on the mass (or volume and density of object) and acceleration due to gravity.
2. Upthrust of fluid on the body = Vρg.
   It depends on the volume (V) of immersed portion of object, density (ρ) of fluid and acceleration due to gravity.

Question 22.
The density of turpentine at 293 K is given as 870 kg m^-3 Identify and write the names of substances that sink in turpentine at the same temperature.

Answer:
A substance sink in a liquid, if density of substance is greater than the density of liquid. Therefore, ice, rubber, paraffin wax and bone will sink in turpentine.

Question 23.
When a metallic block is immersed below the surface of a liquid, state and define the upward force acting on it. (CBSE 2014)
Answer:
It is a buoyant force. The upward force exerted by a liquid is known as buoyant force. Buoyant force = Vρg, where V on the metallic block immersed in the liquid is the volume of metallic block immersed in the liquid and ρ is the density of the liquid.

Question 24.
State the condition under which an object floats on the surface of a liquid. What is the volume of the liquid displaced by the object ? (CBSE 2014, 2015)
Answer:
An object floats on the surface of a liquid if upthrust on the body is greater than the weight of the object. Volume of the liquid displaced is equal to the volume of the body.

Question 25.
A cube of side 3 cm is immersed in water and then in saturated salt solution. In which case will it experience a greater buoyant force. If each side of the cube is reduced to 2 cm and then immersed in water, what will be the effect on the buoyant force experienced by the cube as compared to the first case for water. Give reason for each case. (CBSE 2015)
Answer:
Initial volume of cube, V_i = (3 cm)³= 27 cm³
Final volume of cube, V_f = (2 cm)² = 8 cm³

1. Buoyant force = Vρg, where p is the density of liquid. Since density of saturated salt solution is greater than the density of water, therefore, the cube will experience a greater buoyant force in saturated salt solution than in water.
2. Since the volume of the cube decreases, so the cube will experience a less buoyant force in water as compared to the first case.

Based on Archimedes’s Principle

Question 26.
While drawing water from a well, a bucket of water appears to be heavier as it comes out of the water.
Explain giving reasons. (CBSE 2011)

                                                                   Or

Why is a bucket of water lighter when in water than when it is taken out of water ? (CBSE 2011)
Answer:
When the bucket is inside water, its weight is less than its weight in air due to the upthrust of water.

Question 27.
A student took solid bodies of different shapes, sizes and materials and noted down the apparent loss in weight on partially or fully immersing the bodies in different liquids. Based on the observations, he wrote the following conclusions. Which conclusion is incorrect and why ?
(a) Upthrust depends upon the volume of the body immersed and density of liquid.
(b) Upthrust increases as body goes deeper and deeper inside the liquid.
(c) Upthrust depends upon the density of the liquid and acceleration due to gravity.
(d) Upthrust does not depend upon the shape of the vessel in which liquid is filled. (CBSE 2014)
Answer:
Upthrust = Vρg, where V = volume of body immersed in liquid, ρ = density of liquid, g = acceleration due to gravity.
Therefore, conclusion (b) is incorrect as upthrust does not depend on the depth of the body inside the liquid.

Question 28.
If two equal weights of unequal volumes are balanced in air, what wil} happen when these are completely
dipped in water ? (CBSE 2011)
Answer:
When two weights of unequal volumes are dipped in water, buoyant force acting on the weight of larger volume is more than that on the weight of smaller volume. Hence, weight of smaller volume in water is more than the weight of larger volume. Therefore, these weights are not balanced in water.

Question 29.
An object of mass 500 gm is immersed into a measuring jar containing water. The initial level of water in the measuring jar is 50 cc. Due to the immersion of the object, the water level in the measuring jar reaches to 100 cc. Calculate the mass of the water displaced due to the immersion of the object. (CBSE 2012)
Answer:
Mass of water displaced = Volume of immersed portion of object x density of water
= (100 – 50) cm³ x 1 g cm^-3 = 50 g.

Based on Density and Relative density

Question 30.
If a body is compressed to half its previous volume, what will be the effect on its density and why ?
(CBSE 2014)
Answer:

If volume of body becomes half its previous volume, then its density becomes double i.e., two times its previous value.

LONG ANSWER QUESTIONS

Question 1.
(a) State Pascal’s Law.
(b) Define upthrust or buoyant force. Describe an activity to show that a body loses its weight when immersed in a liquid.
Answer:
(a) Pascal’s Law
A great French physicist and mathematician, Blaise Pascal gave a law regarding the pressure exerted by a fluid enclosed in a container. According to this Taw :
“Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel This fact is shown in figure .

The upward force exerted by a liquid on a body which is immersed in the liquid is known as the upthrust or buoyant force.
(b) Expression for Buoyant force or upthrust
Consider a cylindrical object of height h and area of cross-section A immersed completely in a liquid of density ρ (Figure 6).

Let h₁ be the depth of the upper face of the object from the free surface of liquid. h₂ be the depth of the lower face of the object from the free surface of the liquid.
The height of object, h = h₂ – h₁.
Volume of the object, V= Ah                                  ,
The pressure acting on the upper face of the object, P₁ = h₁ρg.
This pressure acts vertically downward on the upper face of the object.
Therefore, force acting on the upper face of the object in vertically downward direction,
F₂ = P₂A = h₂Aρg                                                                   …(1)
The pressure acting on the lower face of the object in vertically upward direction, P₂ = h₂ρg
Therefore, force acting on the lower face of the object in vertically upward direction,

Factors on which buoyant force or upthrust depends
Buoyant force is directly proportional to

1. the volume (V) of the object or body immersed in liquid
2. the density (ρ) of the liquid in which the object or body is immersed.
3. the acceleration due to gravity (g) at the given place.

Buoyancy: The tendency of an object to float in a liquid or the power of liquid to make an object float in it is called buoyancy.

Question 2.
Archimedes Principle has wide application in making ships and submarines. Explain. (CBSE 2013)
Answer:

1. Floatation of Ships: Iron needle is solid and compact. The density of iron is greater than the density of the water. The weight of the needle is greater than the weight of water displaced by the needle. So iron needle sinks in water. On the other hand, iron ship is not solid. It is hollow and filled with air. So, the average density of the ship as a whole is less than the density of the water. Therefore, the immersed portion of the ship displaces water equal to its weight. Hence the ship floats on the surface of water.
2. Floatation of Submarines: Submarines are just like ships. The difference between them is that submarines are provided with ballast tank [i.e., hot air tank in the form of a balloon to make it heavier). When ballast tank is empty, submarine acts as a ship. Under this condition, the submarine displaces more weight of sea water than its own weight. Hence, it floats in the sea water.
   When the submarine is to dive in water, the doors of the ballast tank are opened. The water enters into the ballast tank and increases the weight of the submarine. When the weight of the submarine becomes more than the weight of the water displaced by it ; it sinks in water.
   To take the submarine again on the surface of water, the compressed air is allowed to enter the ballast tank As a result of this, the water from the ballast tank is forced out. Therefore, the ballast tank is emptied. Again the submarine behaves as a ship and begins to float on the surface of the sea water.

Hope given Previous Year Question Papers for CBSE Class 9 Science Chapter 16 Floatation are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 9 Force and Laws of Motion Class 9 Science Important Questions with Answers PDF will help you in scoring more marks in your exams.

Force and Laws of Motion Class 9 Important Questions and Answers Science Chapter 9

VERY SHORT ANSWER QUESTIONS

Based on force and inertia

Question 1.
Name the physical quantity, which changes the shape of a ball.
Answer:
Force.

More Resources

• Previous Year Question Papers for CBSE Class 9 Science
• NCERT Solutions for Class 9 Science
• NCERT Exemplar Solutions for Class 9 Science
• Value Based Questions in Science for Class 9
• HOTS Questions for Class 9 Science

Question 2.
Define the term force. (CBSE 2011, 2012, 2014)
Answer:
A force is a physical quantity which causes or tends to cause a motion in an object at rest or changes or tends to change the direction of motion of a moving object or the shape or size of the object.

Question 3.
Define balanced forces. (CBSE 2013)

Or

State the meaning of balanced forces. (CBSE 2012)
Answer:
Two equal and opposite forces acting simultaneously on an object are known as balanced forces. The resultant force due to balanced forces is zero.

Question 4.
Define unbalanced forces. (CBSE 2013)
Answer:
Two forces of unequal magnitudes and acting in opposite directions on an object simultaneously are known as unbalanced forces. The resultant force due to unbalanced forces is non zero.

Question 5.
Name the force which is responsible for change in position or state of an object. (CBSE 2012, 2013)
Answer:
Unbalanced force.

Question 6.
A ball is moving over a horizontal smooth surface with a constant velocity. What type of forces are acting on the ball ?
Answer:
Balanced forces are acting on the ball.

Question 7.
An unbalanced force is acting on an object. List two possible effects that will be caused in the motion of object.
(CBSE 2011)
Answer:

1. Object may be accelerated or retarded,
2. Direction of motion of the object may change.

Question 8.
What do you mean by inertia ? (CBSE 2010, 2012)
Answer:
The tendency of a body to oppose any change in its state of rest or uniform motion is called inertia of the body.

Question 9.
Write the kinds of inertia. (CBSE 2012)
Answer:

1. Inertia of rest,
2. Inertia of motion
3. Inertia of direction.

Question 10.
Name the physical quantity that measures inertia. (CBSE 2010, 2012, 2015)
Answer:
Mass of the body measures its inertia.

Question 11.
On which factor does inertia depend ? (CBSE 2013, 2015)
Answer:
It depends on the mass of the object.

Question 12.
Which has more inertia : a man or a child ?
Answer:
A man has more inertia than a child.

Question 13.
Which has highest inertia : solid made of aluminium, steel and wood oÇ same shape and same volume ?
(NCERT Question Bank, CBSE 2011, 2012)
Answer:
Solid made of steel has the highest inertia because its mass is greater than aluminium and wooden solids.

Question 14.
Name the property of bodies to resist a change in their velocity. (CBSE 2012, 2013, 2014)
Answer:
Inertia.

Question 15.
In a tug of war, the rope does not move in any direction. Why ? (CBSE 2013)
Answer:
Because balanced forces act on the rope. Both the teams apply equal and opposite forces on the rope.

Question 16.
Which one has greater inertia : a stone of mass 1 kg or a stone of mass 5 kg ?
Answer:
Inertia depends on the mass of the object. A stone of mass 5 kg has greater inertia than the stone of mass 1kg.

Question 17.
What kind of force is required to accelerate the motion of an object ?
Answer:
Unbalanced force.

Question 18.
A ball is moving over a horizontal smooth surface with a constant velocity. What type of forces are acting on the ball ?
Answer:
Balanced forces.

Question 19.
Name the forces (type of forces) when their resultant force acting on a body is not zero.
Answer:
Unbalanced forces.

Question 20.
Mention any two affects of force.
Answer:

1. It changes the state of rest or motion of a body,
2. It changes the shape of the body.

Question 21.
Is force a scalar or a vector quantity ?
Answer:
Force is a vector quantity.

Question 22.
State Newtons first law of motion.
                  Or
Define the first law of motion.
                 Or
State the law of inertia.
Answer:
Everybody continues in its state of rest or uniform motion in a straight line unless some external force acts on it.

Question 23.
Which law of motion defines the force ?
Answer:
First law of motion.

Question 24.
Define momentum and give its SI unit. (CBSE 2010, 2011, 2012, 2014, 2015)
Answer:
Momentum = mass x velocity.
SI unit of momentum is kg m s^-1.

Question 25.
Name the factors on which momemtum of a body depends. (CBSE 2012, 2013, 2015)
Answer:

1. Mass of the body and
2. Velocity of the body.

Question 26.
Define momentum of a body. (CBSE 2010, 2011)
Answer:
Momentum of a body is defined as the product of the mass and velocity qf the body. Momentum of body = m x v.

Question 27.
Is momentum a scalar or a vector quantity ? (CBSE 2015)
Answer:
Momentum is a vector quantity.

Question 28.
What is the name given to the product of mass and velocity of a body ? (CBSE 2012)
Answer:
Linear momentum.

Question 29.
State Newtons second law of motion. Give its mathematical expression. (CBSE 2010, 2012, 2013)
Answer:
The rate of change of momentum of a body is directly proportional to the unbalanced force acting on it and the change in momentum takes place in the direction of the unbalanced force. F = ma.

Question 30.
Name the physical quantity which is determined by the rate of change of linear momentum.
(CBSE 2010, 2012, 2013)
Answer:
Force.

Question 31.
Define one unit of force. (CBSE 2010, 2011, 2013)
Answer:
A force is said to be unit force if it produces unit acceleration in a body of unit mass.

Question 32.
Name the unit of force in SI.
Answer:
newton (N).

Question 33.
Define SI unit of force. (CBSE 2011, 2014)
Or
Define one newton of force. (CBSE 2012)
Answer:
SI unit of force is newton. Force is said to be 1 newton if it produces 1 m s^-2 acceleration in a body of 1 kg.

Question 34.
What is the relationship between force and acceleration ? (CBSE 2012, 2013)
Answer:
F = ma, where m is the mass of a body.

Question 35.
What is the name given to the product of mass and acceleration of a body ?
Answer:
Force (∴ F = ma)

Question 36.
How much force acts on a body whose momentum is constant (i.e. p = constant) ?
Answer:
F = dp/dt. If p = constant, then no force acts on the body.

Question 37.
Calculate the force required to produce an acceleration of 2.5 m s^-2 in a body of 4 kg.
Answer:
F = ma = 4 x 2.5 = 10 N.

Question 38.
A body of mass 30 kg has a momentum of 150 kg m s^-1. Find its velocity. (CBSE 2013, 2014)
Answer:

Question 39.
An athlete always runs some distance before taking a jump. Why ?
Answer:
To gain the momentum so that he may jump higher.

Question 40.
An object is thrown vertically upward. What is its momentum at the highest point ? (CBSE 2012)
Answer:
Momentum = mass x velocity.
Since velocity of the object at the highest point is zero, so momentum of the object is zero at the highest point.

Question 41.
What will happen to the momentum of a body whose velocity is doubled ?
Answer:
Momentum = mV. Therefore, momentum of a body is doubled if its velocity is doubled.

Question 42.
Name the physical quantity whose SI unit is “newton”.
Answer:
Force.

Question 43.
Which would require a gereater force — accelerating a 1kg mass at 10 m s or a 2 kg mass at 4 m s ?
Answer:
F = ma,
F₁ = 1 x 10 = 10 N and
F₂ = 2 x 4 = 8 N
So, 1 kg mass accelerating at 10 m s^-2 requires greater force than the 2 kg mass at 4 m s^-2.

Or

Which would require a greater force — accelerating a 2 kg mass at 5 m s^-2 or a 5 kg mass at 3 ms^-2 ?
Answer:
F₁ = m₁ x a₁ =2 x 5 = 10 N,
F₂ = m₂ x a₂ = 5 x 3 = 15 N
∴ F₂ > F₁

Question 44.
If the mass of a body is doubled, what will happen to its acceleration, if the applied force remains constant ?
Answer:
a = F/m. If mass(m) is doubled, acceleration becomes half of its original value, if the applied force remains m constant.

Question 45.
State Newtons third law of motion.
Answer:
To every action, there is equal and opposite reaction.

Question 46.
State action and reaction while a person walks on a ground.
Answer:
Action : Force exerted by person on ground.
Reaction : Force exerted by ground on person.

Question 47.
Do action and reaction forces act on same body or different bodies ?
Answer:
Action and reaction act on the different bodies.

Question 48.
State action and reaction in the case when a person swims.
Answer:
Action : Force with which swimmer pushes the water in the backward direction with his hands.
Reaction : The force with which water pushes the swimmer in the forward direction.

Question 49.
State action and reaction in the case when a bullet is fired from the gun. (CBSE 2011)
Answer:
Action : Force exerted by a spring on the bullet.
Reaction : Force exerted on the gun.

Question 50.
State action and reaction when a bullet is fired from the gun.
Answer:
Force exerted on the bullet is action and the force exerted on the gun is reaction.

Question 51.
When a man jumps out from a boat to the bank of a river, the boat moves backwards. Identify the action and reaction in this situation. (CBSE 2015)
Answer:
Action = force with which the foot of the man pushes the boat in the backward direction.
Reaction = force exerted by the boat on the man.

Based on the law of conservation of momentum

Question 52.
State law of conservation of momentum. (CBSE 2010, 2012, 2013, 2015)
Answer:
The total momentum of a system remains constant if no external force acts on the system.

Question 53.
A fast moving truck loses momentum equal to 2 kg m s^-1 after colliding with a stationary car.
Will the car lose or gain momentum ?
How much momentum is lost or gained by the car if the truck comes to the rest after collision ?
Answer:
The car will gain momentum. Momentum gained by the car = 2 kg m s^-1

Question 54.
Name the principle on which a rocket works. (CBSE 2012, 2013)
Answer:
Law of conservation of linear momentum.

Question 55.
What do you mean by recoil velocity of a gun ?
Answer:
The velocity with which a gun moves backward after firing a bullet is called the recoil of the gun.

Question 56.
Is momentum a scalar or a vector quantity ? (CBSE 2015)
Answer:
Momentum is a vector quantity.

SHORT ANSWER QUESTIONS

Based on force and inertia

Question 1.
When are the forces acting on a body said to be balanced ? Give an example. What type of change can the balanced forces bring about in an object ? (CBSE 2010, 2015)
Answer:
Two forces of equal magnitude but acting in opposite directions on a body are said to be balanced forces. When we push a wall but the wall does not move at all, then balanced forces are acting on the wall. When balanced forces are -acting on an object, there is no change in the state of the object.

Question 2.
What are the changes that a force can bring about on a body?  Give examples. (CBSE 2010, 2011)

Or

Explain any three effects that can be produced by force with examples. (CBSE 2012, 2013, 2014)
Answer:
Force can change

1. the shape of the body,
2. direction of motion .of the body,
3. the speed of the body and
4. size of the body

Examples :

1. The shape of a ball lying on a floor can be changed by pressing it.
2. The direction of motion of moving ball can be changed by hitting it with a bat.
3. A ball at rest can be set in motion if force is applied on it.
4. The length of a spring tied at one end can be increased by pulling it.

Question 3.
Two balls A and B of masses m and 2m are in motion with velocities ‘2V’ and ‘V’ respectively.
Compare
(i) their inertia,
(ii) their momentum and
(iii) the force needed to stop them in the same time.
Answer:

(iii) Since momentum of both the balls is same, so same amount of force is needed to stop them in the same time.

Question 4.
Property of a body by virtue of which it opposes any change in state is called
(a) momentum
(b) energy
(c) inertia
(d) acceleration.
Answer:
(c)

Question 5.
If A and B are two bodies with masses 10 kg and 50 kg respectively, then which body has more inertia ? Also calculate the ratio of the inertia of two bodies.
Answer:
Inertia of body B is more than the inertia of body A.
body A 10 kg and body B 50 kg.
If the time taken to bring a ball to rest from a certain velocity V is reduced to half, what will be the change in values of

Question 6.
Look at the diagrams given (Figure A) and answer the following questions. In which case will the object move and in which direction ? Give reason in support of your answer.

Answer:
In case (ii) object moves in the direction of force of 25 N because in this case the net force acting on the object = 25N-15N=10N
In case (i), net force acting on the object is zero.

Question 7.
In the given experimental set-up (Figure B) a student gave the card a sharp, fast horizontal flick with a finger.

1. What will happen to the coin ?
2. Write reason for your answer.

Answer

1. The coin will fall into the glass.
2. The card will move, when a fast horizontal flick with a finger is given to it. On the other hand, coin remains at rest due to inertia of rest and hence falls into the glass.

Question 8.
State the effect of force in each of the following cases,

1. A spring is stretched,
2. A hockey player hits an incoming ball
3. A football lying on the ground is kicked.

Answer:

1. Length of spring increases and hence its shape is changed.
2. The direction of the ball is changed.
3. Football comes in motion from rest state.

Question 9.
(a) Initial and final momentum
(b) Change of momentum
(c) Rate of change of momentum.
Answer:
(a) Initial and final momentum remain the same as they do not depend on time.
(b) Change in momentum remains the same as change in momentum = Final momentum-initial momentum.
(c)

therefore, rate of change of momentum is Time taken doubled if time is reduced to half.

Question 10.
While riding on the bicycle if we stop paddling, why does the bicycle begin to slow down ?
Answer:
Bicycle begins to slow down as its motion is opposed by the unbalanced force known as force of friction between the types of bicycle and the road.

Based on Newton’s laws of motion

Question 11.
What happens when a wet piece of cloth is shaken ? (CBSE 2011)
Answer:
When a wet piece of cloth is shaken, fibres of the cloth come in motion and water droplets in the cloth fall down due to inertia of rest.

Question 12.
A person getting down from the moving bus falls in the direction of the bus. Explain, why ?

Or

A passenger has to run along with moving bus in the same direction of the bus while getting down from the bus. Explain.

Or

It is is dangerous to jump out of a moving bus. Why ? (CBSE 2011, 2013)
Answer:
As soon as the passenger gets down from a moving bus, his foot comes to rest but upper portion of his body remains in motion in the direction of the moving bus. He may fall down if he does not run along with the bus.

Question 13.
A stone tied to a string whirls in a horizontal circle. It flies off tangentially when the string breaks suddenly.
Answer:
The stone flies off tangentially due to inertia of direction of motion.

Question 14.
What happens to a person travelling in a bus when the bus takes a sharp turn ? Explain.(CBSE 2011)

Or

A passenger in a moving car slips to one side of the seat when the car takes a sharp turn. Give reason for it. (CBSE 2012)
Answer:
When car or bus takes a sharp turn, passenger slips to one side of the seat due to the inertia of motion.

Question 15.
It is difficult to balance our body when we accidendy step on a peel of banana. Explain, why ?(CBSE 2011)
Answer:
When we walk on the ground, our foot pushes the ground in the backward direction (Action). On the other
hand, ground pushes our foot in the forward direction (Reaction). This reaction of the ground helps us to move in the forward direction.
But, when our foot falls on a peel of banana, then our foot slips on the peel of banana and cannot push the ground in the backward direction. Consequently, no reaction force acts on our foot. Hence we lose the balance and fall down.

Question 16.
Why are the wheels of vehicle provided with mud gaurds ? (CBSE 2012)
Answer:
The rotating wheels of a vehicle throw out mud sticking to it tangentially due to inertia of direction. The mud
gaurds stop this mud to fall on another vehicle just moving behind the vehicle.

Question 17.
All the cars are provided with seat belts. Give reason. (CBSE 2012, 2013)
Answer:
When a car stops suddenly, driver and passengers continue to move due to inertia of motion. Hence, they may
be hurt due to the collision between them and the body of the car. Therefore, seat belts are provided to prevent their forward motion in case of an accident.

Question 18.
A heavy leather ball and a light tennis ball are kept on the floor of a moving train. When train is suddenly stopped, they are set in motion. In which direction will they move ? Which one of them will attain higher velocity ?
Answer:
They will move in the direction of the motion of the train due to inertia of motion. The mass, of leather ball is greater than that of tennis ball, so leather ball will resist more than the tennis ball to change its state of motion. Hence, tennis ball will attain higher velocity.

Question 19.
A bullet fired on a glass window makes a fine hole while a stone smashes when hits it. State the reason.
(CBSE 2015)
Answer:
A bullet fired from a gun makes a small hole in the window pane while passing through it, but the stone striking the window pane breaks it into pieces. When a bullet strikes the window pane, only a small portion of the window pane where the bullet strikes comes in motion because the bullet makes contact with the pane for a very short time due to its high speed. On the other hand, the remaining portion of the window pane remains at rest due to inertia of rest. Thus, a small hole is made by the bullet in the window pane.
The speed of the stone is very small compared to the speed of the bullet. So the stone makes contact with the window pane for longer period of time. During this-longer time, the whole window pane comes in motion and hence breaks into pieces.

Question 20.
If the net external force acting on a body is zero, then total momentum of the body is
(a) Zero
(b) Variable
(c) Constant
(d) Information not sufficient.
Answer:

Question 21.
A body of mass ‘m is moving with a velocity u. When a force is applied on it for time t, its velocity increases to ‘v’. Write expressions for
(a) Initial and final momentum,
(b) Change in momentum
(c) Rate of change of momentum. Also write SI unit for each
(CBSE 2015)
Answer:
(a) Initial momentum = mu
Final momentum = mv
(b) Change in momentum = final momentum – initial momentum = (mv – mu) = m(v – u)

SI unit of initial momentum, final momentum and change of momentum is kg m s^-1
SI unit of rate of change of momentum is kg m s^-2 or N.

Question 22.
If the time taken to bring a ball to rest from a certain velocity v is reduced to half, what will be the change in values of :
(a) Initial and final momentum
(b) Change of momentum
(c) Rate of change of momentum.
Answer:
(a) Initial and final momentum remain the same as they do not depend on time.
(b) Change in momentum remains the same as change in momentum = Final momentum – initial momentum
(c)

∴ Rare of change of momentum is doubled if time is reduced to half.

Question 23.
Derive First law of motion mathematically from the mathematical expression of Second law of motion.
Answer:
According to First law of motion, a body continues to move with uniform velocity or zero acceleration if no external force acts on it. Second law of motion is given by F= ma.
If F = 0, a = 0. This is the mathematical expression of first law of motion.

Question 24.
Why, no force is required to move an object with a constant velocity ? (CBSE 2011)
Answer:
We know, F = ma
When, velocity is constant, then acceleration, a = 0
Hence, F = 0

Question 25.
A cricket player lowers his hands while catching a fast moving ball. Explain. Why ?
(CBSE 2011, 2012, 2013)
Answer:
A cricket player lowers his hands while catching the ball.
F = dp/dt
If a player does not lower his hands while catching the ball, the time to stop the ball is very small. So a large force has to be applied to reduce the velocity of the ball to zero or to change the momentum of the ball. When a player lowers his hands, the time to stop the ball is increased and hence less force has to be applied to cause the same change in the momentum of the ball. Therefore, the hands of the player are not injured.

Question 26.
Explain, how can we walk easily on a hard and rough surface than on a slippery surface ?
Answer:
Walking of a person. When a person walks on the ground, he pushes the ground with his foot in the backward direction by pressing the ground. This push is known as action. According to Newtons third law of motion, an equal and opposite reaction acts on the foot of the person by the ground. This reaction (force) of the ground on the person pushes him forward (figure 21).
Thus, Action = force exerted on the ground by a person through his foot.

Question 27.
Two similar buses are moving with same velocity on the road. One of them is empty and the other is loaded with passengers. Which of the two will be stopped by the application of less force ? Explain.
(CBSE 2010, 2011, 2013)
Answer:
Momentum = m v. Loaded bus has greater mass than the empty bus. So loaded bus has greater momentum than the empty bus. The rate of change momentum is directly proportional to the force applied. Therefore, the empty bus will be stopped by applying less force.

Question 28.
A bullet fired from a gun is more dangerous than an air molecule hitting a person, though both bullet and air molecule are moving with same velocity. Explain.
Answer:
The momentum of a bullet is very large than the momentum of the air molecule as the mass of bullet is very large than that of air molecule. When bullet and air molecule hit a person, then the momentum transferred to person by a bullet is very large than the momentum transferred by the air molecule. Hence, large force is exerted on the person by the bullet.

Question 29.
When a force acts on an object, it accelerates ? What do you observe, when two equal and opposite forces act on an object ? (CBSE 2011)
Answer:
When two equal and opposite forces act on an object, then the net force acting on it is zero. Therefore, the object will remain at rest if it were at rest before the application of two equal and opposite forces. However, the object will continue to move with constant velocity if it were moving with constant velocity before the application of the forces.

Question 30.
Draw velocity-time graph of a moving particle on which net external force acting is zero.
Answer:
Net external force = zero. It means, acceleration (a = F/m) of the particle is zero.

In other words, particle is moving with constant velocity. Velocity-time graph of such a particle is represented by a curve AB parallel to time-axis (Figure C)

Question 31.
Draw distance-time graph of a moving object on which net external force acting is zero.
Answer:
Net external force = zero. It means, acceleration (a = F/m) of the particle is zero.

In other words, the object is moving with constant velocity. Therefore, the particle travels equal distances in equal intervals of time. Distance time graph of such an object is shown in figure D.

Question 32.
Glass wares are wrapped in straw during their transportation. Give reason.
(CBSE 2012)
Answer:
During transportation, the glass wares may break if they collide with each other in the event of jerks. When they are wrapped in straw, the force of jerk is transmitted to them through the pieces of straw in a longer period of time. Thus, the change in momentum of the glass wares takes place in a longer period of time. Therefore, a very small force is experienced by them in the event of jerks and hence they do not break.

Question 33.
When two bodies X and Y collide with each other, X exerts a force of 5 N on Y towards east direction. What
is the force exerted by Y on X ? Justify your answer stating the law. (CBSE 2012)
Answer:
Force exterted by Y on X = 5 N towards west direction as per Newton’s third law of motion.

Question 34.
Explain, how a Karate player can break a pile of tiles with a single blow of his hand. (CBSE 2012)
Answer:
A Karate player strikes the pile of tiles very fast so that change in the momentum of his hand takes place in
very small time interval. Hence, a very large force (F = dp/dt) is exerted on the pile of tiles, which is enough to break the pile of tiles.

Question 35.
Why a glass pane of a window is shattered when a flying pebble hits it ? (CBSE 2012)
Answer:
When a flying pebble hits the glass pane, its contact time with glass pane is large. During this large interval of time, it imparts its momentum to the entire glass pane, which in turn shattered.

Question 36.
A truck of mass M is moved under a force F. If the truck is loaded with an object equal to the mass of the truck and the driving force is halved, then how does the acceleration change ?
Answer:
Acceleration, a = F/m. When m is doubled and F is made half, acceleration becomes ¼ th of its initial value.

Question 37.
Why are road accidents at high speed very much worsen than accidents at low speeds ?
Answer:
When accidents at high speed occur, then large momentum is to be changed in small interval of time. Hence, large force is exerted on vehicles and they get damaged very badly as compared to when accidents occur at low speed.

Question 38.
Name the physical quanity whose unit is

1. kg m s^-2 and
2. kg m s^-1

Answer:

1. Force,
2. Linear momentum

Question 39.
Represent the following graphically :
(a) momentum versus mass, when velocity is constant
(b) momentum versus velocity, when mass is constant.
Answer:
(a)

(b)

Question 40.
Describe in brief an activity to illustrate the properly of inertia of rest.
Answer:

1. Describe an activity to demonstrate the property of inertia of rest of an object.
2. Now place a fifty paisa coin on the card board.
3. Strike the card board with a finger.

It is found that card board flies away and the coin falls into the glass. This is because, card board moves away due to the application of force of finger. However, coin remains at its position due to inertia of rest and hence falls into the glass.
This activity demonstrates the property of inertia of rest of an object. It is based on Newton’s first law of motion.

Question 41.
In the figure below, the card is flicked with a push.

(a) What do you observe in above case and why ?
(b) State the law involved in this case.
(c) What will be your observation if the above coin is replaced by a heavy five rupee coin. Justify your answer.
Answer:
(a) The coin falls into the glass. The card comes in motion due to push but coin on the card remains at rest. The coin falls into the glass due to inertia of rest.
(b) Law of inertia or First law of motion.
(c) Heavy coin will also fall into the glass. The heavy coin has more inertia than the lighter coin.

Question 42.
State Newton’s Third law of motion. Are the forces mentioned in the law balanced forces ? Why ? Will they always produce accelerations of equal magnitude ? Why ?
Answer:
For every action, there is equal and opposite reaction. Forces are not balanced forces because both the forces act on two different bodies. They do not produce the same acceleration because acceleration = ~~. Since masses (m) of both the bodies are different, so accelerations of both the bodies are different.

Question 43.
When a person hits a stone, his foot is injured. Why ? (CBSE 2011)
Answer:
When a person hits a stone, the stone exerts equal force on his foot. Due to this force, his foot gets injured.

Question 44.
According to Newton’s third law of motion, a ball falling towards earth exerts a force on the earth but the motion of earth towards the ball is not noticed. Explain why ?
Answer:
The acceleration produced in the earth is very small as its mass is very large. Hence, the motion of the earth towards ball is not noticed.

Question 45.
How a man can swim in water ?

Or

A swimmer is able to swim in a forward direction in a swimming pool only when he is pushing the water in the backward direction. Give reason for the above mentioned statement and justify the same. (CBSE 2013)
Answer:
When a swimmer pushes water in the backward direction with his hands, equal and opposite reaction by water on the man pushes him in the forward direction.

Question 46.
When a person jumps out of a boat, the boat moves backward. Explain, why ? (CBSE 2011, 2012)
Answer:
When a person jumps out of a boat, he pushes the boat in the backward direction (Action). According to Newtons third law of motion, the boat exerts an equal force (i.e. reaction) on the person in the forward direction. So, when the person jumps out of the boat, the boat moves backward (Figure 23). Thus, Action = force applied by the person on the boat through his foot. Reaction = force exerted on the person by the boat.

Question 47.
Why a boatman pushes the bank of the river with a pole to take his boat into the river ?
Answer:
A boatman pushes the river bank with a bamboo pole to take his boat into the river.
When the boatman pushes the river bank with a bamboo pole, the river bank offers an equal and opposite reaction. This reaction helps the boat to move into the river. In this case, action = force applied on the ground with a bamboo pole, and reaction = force exerted by the ground on the boat.

Question 48.
“Action and reaction are equal and opposite but even then they do not cancel each other.” Explain, why ?
(CBSE 2011)

Or

Why don’t, the forces of action and reaction cancel each other ? (CBSE 2013)
Answer:
Two equal and opposite forces can cancel each other if they act on the same body. But action and reaction do not act on the same body. Action acts on one body and the reaction acts on another body. Hence they cannot cancel each other.

Question 49.
Look at the diagram and answer the following questions :

(a) When a force is applied through the free end of the spring balance A, the reading on the spring balance A is 15 g wt. What will be the measure of the reading shown by spring balance B ?
(b) Write reasons for your answer.
(c) Name the force which balance A exerts on balance B and the force of balance B on balance A.
Answer:
(a) Reading shown by spring balance is 15 g wt.
(b) Every action has equal and opposite reaction.
(c) Force which balance A exerts on balance B is action. Force of balance B on balance A is reaction.

Question 50.
A man throws a ball weighing 500 g vertically upwards with a speed of 10 m s^-1
(i) Find its initial momentum
(ii) Find its momentum at the highest point of its flight.
Answer:

Question 51.
A person is hit harder, when he falls on a hard floor than when he falls on the heap of sand or cotton. State the reason. (CBSE 2015)
Answer:
According to Newton’s second law of motion,

When a person falls on a hard floor, his change in momentum occurs in small interval of time because he comes to rest abruptly. Hence, a large force is exerted on the person by the floor. On the other hand, when the person falls on a heap of sand or cotton, the sand or cotton yields under his weight. Therefore, the change in momentum of the person occurs in a large interval of time. Hence, less force is exerted on the person by the heap of sand or cotton.

Question 52.
Mention any two examples which can be explained on the basis of Third law of motion.
Answer:

1. Walking of a person on a road,
2. Recoil of a gun.

Based on the law of conservation of momentum

Question 53.
Why does a gun recoil backward when a bullet is fired from it ?

Or

Firing a bullet from a gun, results in recoil of gun. Give reason. (CBSE 2011)
Answer:
A gun recoils, when a bullet is fired from it to conserve the linear momentum of the gun and the bullet.

Question 54.
A gun recoils backward with small speed than the bullet moving forward. Explain why ?
Answer:
Recoil speed of gun is inversely proportional to the mass of the gun. Mass of gun is much greater than the mass of bullet. Therefore, gun recoils backward with small speed than the bullet moving forward.

Question 55.
Explain, why an inflated balloon lying on the surface of a floor moves forward when pierced with a needle.
Answer:
When balloon is pierced with a needle, air inside the balloon rushes out with certain momentum. Therefore, the balloon moves in the opposite direction to conserve the linear momentum of the balloon.

Question 56.
When a bullet is fired, it exerts an equal and opposite force on the gun, yet hurt caused by the recoil of the
gun is much less than that by a bullet ? Give reason. (CBSE 2012)
Answer:
Recoil velocity of gun is much less than the velocity of bullet. Therefore, momentum imparted by gun is very small and hence it hurts less than that of the bullet.

Question 57.
Mention two examples from your daily life which can be explained on the basis of law of conservation of momentum. (CBSE 2013)
Answer:

1. Recoil of a gun,
2. Rocket propulsion.

Question 58.
Two friends on roller skates are standing 5m apart facing each other. One of them throws a ball of 2 kg towards the other, who catches it ? How will this activity affect the positions of the two ? Explain.
Answer:
Total initial linear momentum of the two friends is zero as both are at rest. When one person throws the ball towards the other and the other catches it, then the total linear momentum of both will have to be zero as no external force acts on them. Thus both friends must move in opposite direction. Hence, the distance between both friends will increase.

Question 59.
Observe the following diagram and answer the questions given below :

Which direction does the balloon move when the thread tied to its neck is removed and why ?
State the conclusion drawn from this activity.
Answer:
When the thread tied to its neck is removed, air inside the balloon rushes to the left side and the balloon moves to right side to conserve linear momentum.
Law of conservation of linear momentum is verified.

Question 60.
A gunman gets jerk in backward direction while firing a gun. State the reason. (CBSE 2015)
Answer:
The gun recoils backward to conserve the momentum of the system (gun + bullet). The backward motion of the gun exerts a force on the gunman and hence he gets a jerk in the backward direction.

LONG ANSWER QUESTIONS

Question 1.
State Newtons second law of motion. Use this law to find the method to measure force acting on an object.
(CBSE 2010, 2011)

Or

From Newton’s second law of motion, obtain a mathematical expression for force. (CBSE 2013)
Answer:
According to this law, the change in momentum of a body per unit time (i.e. rate of change of momentum) is directly proportional to the unbalanced force acting on the body and the change in momentum takes place in the direction of the unbalanced force on the body.
∴ F ∞ dp/dt
Consider a body of mass moving with initial velocity Let a force acts on the body for time so that the velocity of the body after time is .
Initial momentum of the body, p_i = mu
Final momentum of the body, p_f = mv
Now, change in momentum of the body = p_f – p_i = mv – mu = m(v-u)

Thus, force acting on the body is directly proportional to (i) its mass (m) and (ii) its acceleration (a).
Eqn. (1) gives the mathematical form of Newtons second law of motion. The force given by eqn (1) acts on the body.
Newton’s second law of motion in vector form     
We know, force ( F ) and acceleration ( a ) are vector quantities, whereas mass ( m)  is a scalar quantity. Therefore, Newton’s second law of motion can be written in vector form as

This relation shows that the direction of force applied on the body is same as that of the acceleration produced in the body.

Question 2.
Define momentum of a body. Prove with the help of third law of motion that the total momentum of two bodies is conserved during collision provided no external force acts. (CBSE Sample Paper)
Answer:
According to the law of conservation of momentum, the total momentum of a system (or an object) remains constant if no net external unbalanced force acts on the system.
That is, momentum of a system, p = constant, if net external force acting on it is zero (i.e. F = 0).
Consider a system consisting of two bodies A and B of (say glass spheres) masses m₁ and m₂ respectively. Let these bodies are moving with velocities u₁ and u₂ as shown in figure 26. Let u₁ > u₂ Let these bodies collide with each other for a small interval of time ‘dt’. At the time of collision, body A exerts a force F on body B and body B exerts equal and opposite force (- F) on body A. Due to these forces, the momentum of the bodies changes. Let v₁ and v₂ be the velocities of body A and body B respectively after the collision.



i.e. Total momentum of the system (i.e. bodies A and B) before collision = Total momentum of the system (i.e. bodies A and B) after collision. This is the law of conservation of linear momentum.

Question 3.
From Newton’s second law of motion,

From this establish F = ma, where m is mass and a is acceleration. (CBSE 2011)
Answer:
Consider a body of mass moving with initial velocity Let a force acts on the body for time so that the velocity of the body after time is .
Initial momentum of the body, p_i = mu
Final momentum of the body, p_f = mv
Now, change in momentum of the body = p_f — p_i = mv – mu = m(v-u)

Thus, force acting on the body is directly proportional to (i) its mass (m) and (ii) its acceleration (a).
Eqn. (1) gives the mathematical form of Newtons second law of motion. The force given by eqn (1) acts on the body.
Newton’s second law of motion in vector form     
We know, force ( F ) and acceleration ( a ) are vector quantities, whereas mass ( m)  is a scalar quantity. Therefore, Newton’s second law of motion can be written in vector form as

This relation shows that the direction of force applied on the body is same as that of the acceleration produced in the body.

Question 4.
Derive the law of conservation of linear momentum.

Or

Total momentum of two bodies remains unchanged before and after the collision. Justify this statement.
(CBSE 2015)
Answer:
Let a moving ball collides with another stationary ball lying on a ground. Observe, what happens after collision. The moving ball will slow down i.e. its velocity decreases after colliding with the stationary ball. On the other hand, the stationary ball begins to move i.e. its velocity increases after collision.
Consider a system consisting of two bodies A and B of (say glass spheres) masses m₁ and m₂ respectively. Let these bodies are moving with velocities u₁ and u₂ as shown in figure 26. Let u₁ > u₂ Let these bodies collide with each other for a small interval of time ‘dt’. At the time of collision, body A exerts a force F on body B and body B exerts equal and opposite force (- F) on body A. Due to these forces, the momentum of the bodies changes. Let v₁ and v₂ be the velocities of body A and body B respectively after the collision.



i.e. Total momentum of the system (i.e. bodies A and B) before collision = Total momentum of the system (i.e. bodies A and B) after collision. This is the law of conservation of linear momentum.

Question 5.
State and verify law of conservation of momentum. (CBSE 2013)
Answer:
Consider a system consisting of two bodies A and B of (say glass spheres) masses m₁ and m₂ respectively. Let these bodies are moving with velocities u₁ and u₂ as shown in figure 26. Let u₁ > u₂ Let these bodies collide with each other for a small interval of time ‘dt’. At the time of collision, body A exerts a force F on body B and body B exerts equal and opposite force (- F) on body A. Due to these forces, the momentum of the bodies changes. Let v₁ and v₂ be the velocities of body A and body B respectively after the collision.



i.e. Total momentum of the system (i.e. bodies A and B) before collision = Total momentum of the system (i.e. bodies A and B) after collision. This is the law of conservation of linear momentum.

Hope given Previous Year Question Papers for CBSE Class 9 Science Chapter 9 Force and Laws of Motion are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 11 Work, Power and Energy Class 9 Science Important Questions with Answers PDF will help you in scoring more marks in your exams.

Work, Power and Energy Class 9 Important Questions and Answers Science Chapter 11

VERY SHORT ANSWER QUESTIONS

Based on work done

Question 1.
Define the term ‘work done’. (CBSE 2011, 2012, 2015)
Answer:
Definition: Work is said to be done by a force on a body or an object if the force applied causes a displacement in the body or the object.

More Resources

• Previous Year Question Papers for CBSE Class 9 Science
• NCERT Solutions for Class 9 Science
• NCERT Exemplar Solutions for Class 9 Science
• Value Based Questions in Science for Class 9
• HOTS Questions for Class 9 Science

Question 2.
How much work is done by a man who tries to push the wall of a house but fails to do so.
(Similar CBSE 2011, 2013)
Answer:
W = FS = 0 (∴ S = 0)

Question 3.
A body of mass 2 kg is moving in a circular path of radius 2m. How much work is done on the body ?
(CBSE 2011)
Answer:
Zero. This is because centripetal force acting on the body is perpendicular to the displacement of the body (W = FS cos 90° = 0).

Question 4.
What would be the amount of work done on an object by a force, if the displacement of the object is zero ?
Answer:
W = FS = 0 (∴ S = 0)

Question 5.
What is the work done by the earth in moving around the sun ? (CBSE 2011)
Answer:
Zero.

Question 6.
When is work done by a force negative ? (CBSE 2011, 2012, 2014)
Answer:
Work done by a force is negative, when the displacement of the body is in the direction opposite to the direction of the force.

Question 7.
When is work done by a force positive ? (CBSE 2012)
Answer:
Work done by a force is positive, when the displacement of the body is in the direction of the force.

Question 8.
When is work done by a force zero ? (CBSE 2011)
Answer:
Work done by a force is zero, when body is not displaced from its position by the force or when force acting on the body is perpendicular to the direction of the displacement of the body.

Question 9.
Write two conditions under which work is said to be done. (CBSE 2011, 2012)
Answer:

1. Force must act on the body and
2. the body must be displaced from its position either in the direction of applied force or in a direction opposite to the direction of the applied force.

Question 10.
What is SI unit of work ? (CBSE 2015)
Answer:
S.I. unit of work is joule (J).

Question 11.
Write the expression for a work done by a force F acting on an object at an angle θ with the displacement S of the object.
Answer:
W = FS cos θ.

Question 12.
What should be the angle between force and displacement for maximum work ? (CBSE 2013)
Answer:
W = FS cos θ. Work will be maximum if cos θ = 1 or θ = 0°.

Question 13.
Does the work done depend upon how fast an object is raised ? Explain. (CBSE 2013)
Answer:
Work done depends on the force applied and distance travelled by an object. It does not depend on how
fast an object is raised.

Based on energy (Kinetic energy and Potential energy)

Question 14.
Define the “energy”.
Answer:
The capacity of doing work by an object is known as the energy of the object.

Question 15.
What is SI unit of energy ?
Answer:
S.I. unit of energy is joule (J).

Question 16.
Define mechanical energy.

                Or

Name two forms of mechanical energy.
Answer:
Mechanical energy is the sum of Kinetic energy and potential energy.

Question 17.
Define Kinetic energy.
Answer:
The energy possessed by a body by virtue of its motion is called kinetic energy..

Question 18.
What is SI unit of kinetic energy ? Define it.
Answer:
joule (J). Kinetic energy is said to be 1 J if a body of mass 1 kg moves with a speed of 1 ms^-1.

Question 19.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Answer:
Kinetic energy.

Question 20.
What type of energy is possessed by a flowing water ?
Answer:
Kinetic energy.

Question 21.
Identify the energy possessed by a rolling stone. (CBSE 2011)
Answer:
Kinetic energy.

Question 22.
Identify the kind of energy possessed by a running athlete. (CBSE 2011)
Answer:
Kinetic energy.

Question 23.
A car and a truck are moving with the same velocity of 60 km/hr. Which one has move kinetic energy ?
(Mass of truck > mass of car). (CBSE 2011)
Answer:
K.E = 1/2 mv². Since mass of truck is greater than the mass of car and both have same velocity, therefore, K.E. of track > K.E. of car.

Question 24.
What will be the kinetic energy of a body when its mass is made four times and the velocity is doubled ?
(CBSE 2011)
Answer:

Question 25.
If we lift a body of mass 7 kg vertically upwards 10 m, then calculate the force required to lift the body
(g = 10 ms^-2). (CBSE 2011)
Answer:
Force = mg = 7 x 10 = 70 N.

Question 26.
Define potential energy of an object.
(CBSE Sample Paper 2010, CBSE 2011, 2012, 2014, 2016, 2017)
Answer:
The energy possessed by an object by virtue of its position or shape is known as potential energy.

Question 27.
Give an example of body having potential energy due to change of shape. (CBSE 2011)
Answer:
Spring of a watch or stretched bow and arrow.

Question 28.
Name the type of energy possessed by a raised hammer. (CBSE 2011)
Answer:
Potential energy.

Question 29.
State SI unit of potential energy. (CBSE Sample Paper 2010, CBSE 2011, 2014, 2016)
Answer:
joule (J)

Question 30.
Give an example of an object having elastic potential energy. (CBSE 2011)
Answer:
A stretched spring or a compressed spring has elastic potential energy.

Question 31.
In what form, energy is stored in a wrist watch ?
Answer:
Potential energy.

Based on transformation of energy

Question 32.
A torch cell converts one form of energy into another form. Name these two forms of energy.
(CBSE 2011)
Answer:
Chemical energy is converted into electric energy.

Question 33.
A log of wood cut by a saw becomes hot. From where this heat energy comes ?
Answer:
Mechanical energy is converted into heat energy.

Question 34.
When we switch on the electric bulbs, one form of energy is converted into another form. Name these forms of energy. (CBSE 2011)
Answer:
Electrical energy is converted into light and heat energy.

Question 35.
When a ball is thrown vertically upwards, its velocity goes on decreasing. What happens to its potential energy as its velocity becomes zero ? (CBSE 2011)
Answer:
Potential energy of the ball goes on increasing when its kinetic energy decreases. Potential energy becomes maximum and equal to initial kinetic energy when the velocity of the ball becomes zero (provided there is no air resistance).

Question 36.
Write the observed energy transformation that takes place at thermal power station. (CBSE 2011)
Answer:
Chemical energy into heat energy and then to electrical energy.

Question 37.
State the transformation of energy taking place when

1. Green plants prepare their food
2. Head of a nail is hammered hard and it becomes hot. (CBSE 2011)

Answer:

1. Solar energy + Green leaves —> Food (chemical energy)
2. Kinetic energy of hammer is convered into the heat energy (i.e. K.E. —> Heat energy)

Based on conservation of energy

Question 38.
State the law of conservation of energy. (CBSE 2011, 2012)
Answer:
Energy can neither be created nor be destroyed but can be changed from one form into another form.

Based on power and commercial unit of energy

Question 39.
State the physical quantity which will be affected by changing the rate of doing work. (CBSE 2013)
Answer:
Power ( = rate of doing work).

Question 40.
Establish a relationship between SI unit and commercial unit of energy.
                                             Or

Derive the relation between the commercial unit of energy and joules.
Answer:
SI unit of energy is joule and commençai unit of energy is kWh.

Question 41.
Name the commercial unit of electric energy.
Answer:
The commercial unit of electric energy is kilowatt hour (kWh).

Question 42.
State the relation between commercial unit of energy and joule.

                                    Or

How many joules make one kilowatt hour ?
Answer:
Commercial unit of energy is kWh. 1 kWh = 3.6 x 10⁶ J.

SHORT ANSWER QUESTIONS

Based on work done

Question 1.
Distinguish between positive and negative work. When you lift an object, two forces act on it. Identify these forces. Which one of the two does,

1. positive work
2. negative work ? Justify your answer. (CBSE 2012)

Answer:
Work is said be positive if the body is displaced in the direction of the applied force. Work is said to be negative if the body is displaced in a direction opposite to the direction of applied force.
When we lift an object, the forces acting on the object are

1. force of gravity and
2. muscular force.

Force of gravity does negative work as force of gravity acts downwards and the object is displaced upwards. Muscular force does positive work as the object is displaced in the direction of the applied muscular force.

Question 2.
A boy throws a rubber ball vertically upwards. What kind of work is done;

1. by the force applied by the boy,
2. by the gravitational force. Support your answer with reason. (CBSE 2011, 2013)

Answer:

1. Work done by the force applied by the boy is positive as both the applied force and the displacement of the ball are in the same direction.
2. Work done by gravitational force is negative as the force and the displacement of the ball are in opposite direction.

Question 3.
A coolie holding a heavy box is waiting for someone at the bus stand for 15 minutes. How much work has been done by him ? (Similar CBSE 2011)

                                                                                   Or

A person holds a suitcase for 30 minutes and gets tired. Has he done some work or not ? Justify your answer.
(CBSE 2012)
Answer:
Since coolie is applying force on the heavy box to hold it but there is no displacement of the box (i.e. S = 0), therefore, work done by him is zero (∴ W = FS cos θ = 0).

Question 4.
Work done by a coolie on the luggage on his head while carrying it on horizontal road. (CBSE 2013)
Answer:
The force of gravity acting on the box acts vertically downward and the displacement is in the horizontal direction, so θ = 90°. Hence, W = FS cos θ = FS cos 90° = 0

Question 5.
In a tug of war, one team wins and the other team loses. Which team does positive work and which one does negative work ? Justify your answer. (CBSE 2011)
Answer:
Winning team does positive work on the rope because the force applied by the team on the rope acts in the direction of the displacement of the rope. On the other hand, losing team does negative work as the force applied by the team on the rope acts in the direction opposite to the direction of the displacement of the rope.

Based on Kinetic and potential energies

Question 6.
Establish the relationship between kinetic energy and momentum of body. (CBSE 2012)
Answer:
Relationship between kinetic energy and momentum of body

Question 7.
Which would have greater effect on the kinetic energy of an object-doubling the mass or doubling the velocity ? (CBSE 2011
Answer:
K.E. = 1/2 mv² . When mass is doubled, K.E. becomes 2 times its initial value. When velocity is doubled,
K.E. becomes 4 times its initial value. Thus, doubling the velocity would have greater effect on the kinetic energy than doubling the mass.

Question 8.
A bus and a car have same kinetic energy. Which of the two is moving fast ? Explain. (CBSE 2011)
Answer:

Question 9.
Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force. Explain it with an example. (NCERT Question Bank, CBSE 2012)
Answer:

When an object has uniform circular motion, the speed of the object remains the same i.e. v = u. Hence, work done by the force = zero.

Question 10.
The velocity of a body moving in a straight line is increased by applying a constant force F, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body. (CBSE 2011)
Answer:
Consider a body or an object of mass m moving with velocity u. Let a force F be applied on the body so that the velocity attained by the body after travelling a distance S is v (Figure 5).

Work done by the force on the body is given by
W =      FS                                                                               …(i)
Since velocity of the body changes so the body is accelerated. Let a be the acceleration of the body. Therefore, according to Newton’s second law of motion,
F =     ma                                                                             …(ii)
Using eqn. (ii) in eqn. (i), we get

Thus, work done by a force on a body is equal to the change in kinetic energy of the body This is known as work-energy theorem.

Question 11.
Two bodies of same mass start from rest and move with velocities of V and 2V respectively. Find the ratio of their kinetic energies. (CBSE 2012)
Answer:

Question 12.
Two bodies of masses my and m2 have equal kinetic energies. What is the ratio of their linear momenta ?
(CBSE 2012)

                                                                  Or

Two balls have different masses but same kinetic energy. Which has the greater momentum ? Justify.
(CBSE 2013)
Answer:

Thus, momentum of the ball of large mass is more.

Question 13.
Derive an expression for the potential energy of an object of mass m that has been raised to a height ‘h’ from the ground. (CBSE 2011, 2014, 2016)

                                                              Or

Derive an expression for potential energy.
Answer:
The potential energy stored in an object due to its vertical position with respect to the surface of the earth is called gravitational potential energy.
Gravitational potential energy of an object at a height h above the surface of earth is equal to the work done in raising the object through a height h against the gravitational force or gravity.
Consider an object of mass m raised to a height h against gravity (Figure 7).

Minimum force required to lift the object, F = weight of body = mg
Distance travelled by the object, S = h
∴                        Work done, W = F x S = mgh
This work done against force of gravity is equal to the potential energy or gravitational potential energy of the object. i. e., P.E. = mgh
Thus, gravitational potential energy of an object depends upon

1. the weight (mg) of the object and
2. the height (h) of the object from the surface of the earth.
   SI Unit of potential energy is joule (J).

Question 14.
An object is dropped from a height h when is its

1. Potential energy maximum,
2. Kinetic energy maximum. (CBSE 2011)

Answer:

1. Potential energy of the object is maximum, when it is at heigh h.
2. Kinetic energy of the object is maximum, when it just touches the ground.

Based on transformation of energy

Question 15.
The head of a nail becomes warm when it is hammered into a plank of wood. Explain stating the scries of energy transformations taking place. (CBSE 2011)
Answer:
The potential energy of a raised hammer is converted into the kinetic energy when hammer falls down. Then this kinetic energy of the falling hammer is converted^hto heat energy when it strikes the head of a nail. Therefore, the head of the nail becomes warm.

Question 16.
Name the devices which

1. convert chemical energy into electrical energy and
2. light energy into electrical energy.

Answer:

1. A thermal power plant
2. A photocell.

Question 17.
Name the appliances which work under the following energy transformation.

1. Sound energy into electrical energy.
2. Heat energy into mechanical energy. (CBSE 2011)

Answer:

1. Microphone
2. Heat engine.

                                                           Or

Name the appliances which work under the following energy’ transformation :

1. Mechanical energy into electrical energy
2. electrical energy into mechanical energy.

Answer:

1. Electric generator
2. Electric motor.

Question 18.
When a body falls freely, its potential energy is converted into kinetic energy. But when the freely falling body reaches the ground, it comes to rest. What happens to the kinetic energy of the body when it stops on reaching the ground ? (CBSE 2011)
Answer:
When a freely falling body stops on reaching the ground, sound is heard and the ground becomes hot, where the body strikes. So kinetic energy of a freely falling body is converted into sound energy and heat energy. Based on power and commercial unit of energy

Question 19.
A boy and a girl do the same work in 5 minutes and 10 minutes respectively. Which of these two has more power and why ?
Answer:
P = W/t. As the boy takes less time to do the same work as compared to the girl, so power of the boy will be more than that of the girl.

Question 20.
Give mathematical relation between power, force and velocity. (CBSE 2011)
Answer:
P = Fv.

Question 21.
Express Kilowatt in terms of joules per second. (CBSE 2012)
Answer:
1 kilowatt = 1000 W
Since 1 W = 1 J s-1
∴ 1 kilowatt = 1000 J s^-1

Question 22.
Differentiate between kilowatt and kilowatt hour. (CBSE 2011, 2012, 2014)
Answer:
Kilowatt is the unit of power. 1 kilowatt = 1000 J s^-1
Kilowatt hour is the unit of electric energy. 1 kilowatt hour = 3.6 x 10⁶ J

Question 23.
In a house 3 bulbs of 25 W each are used for 5 hours a day. Calculate the units of electricity consumed in a month of 31 days. Also, find the total expenditure if 1 unit of electricity costs Rs. 2.50. (CBSE 2014)
Answer:
Electric energy consumed by 3 bulbs in a day = power x time = 3x 25 x5 = 375 Wh
∴ Electricity consumed in 31 days = 375 x 31 = 11625 Wh =11.625 kWh =11.625 units
∴ Cost of electricity consumed = 11.625 x 2.50 = Rs. 29.06

LONG ANSWER QUESTIONS

Question 1.
Define the term “Work”. State the factors on which work done depends. Derive an expression for the work done by a force applied on an object at an angle 9 with the horizontal direction.

                                                                 Or

Define work. State two factors on which the magnitude of work depends. (CBSE 2011)
Answer:
In our daily life, the word work means any kind of mental and physical activity. For example, we say that we are doing work while

1. reading a book.
2. cooking a food.
3. walking on a level road with a box on our head.
4. pushing a wall of a house but fails to do so.

Factors on which work done depends Work done by a force depends upon :

1. The magnitude of the applied force. If a small force is applied on a body, less amount of work is done. On the other hand, if a large force is applied on the body, more amount of work is done on the body.
   Thus,                     W ∝ F, where F is magnitude of applied force.
2. The distance travelled by the body on the application of force ( i. e., displacement S). If a body travels large distance on the application of force, large amount of work is done. If a body travels a small distance on the application of force, small amount of work is done.
   Thus,                     W ∝ S.

Question 2.
(a) Define the term “energy”. Write the names of different forms of energy.
(b) Define kinetic energy. Derive an expression for the kinetic energy of an object of mass m moving with a velocity V. (CBSE 2011, 2017)
Answer:
(a) Definition of energy : The capacity of doing work by a body or an object is known as the energy of the body or the object.
Unit of Energy: Unit of energy is same as that of the unit of work. So, SI unit of work is joule (J). When we say that energy of a body is 1 joule, it means, this body has the capacity to do 1 joule work.
The various forms of energy are :

1. Mechanical Energy: The sum of kinetic energy and potential energy of a body is known as mechanical energy.
2. Heat or Thermal Energy: The energy possessed by a body due to its temperature is known as heat or thermal energy.
3. Chemical Energy: The energy released in chemical reactions is known as chemical energy.
4. Sound Energy: The energy of a vibrating body producing sound is known as sound energy.
5. Electrical Energy: The energy of moving electrons in a conductor connected with a battery is known as electrical energy.
6. Nuclear Energy: The energy released when two nuclei of light elements combine with each other to form a heavy nucleus or when a heavy nucleus breaks into two light nuclei is known as nuclear energy.
7. Solar Energy: The energy radiated by the sun is known as solar energy.

(b) Definition : The energy possessed by a body by virtue of its motion is known as kinetic energy. In other words, we can say that anything which moves has kinetic energy.
Consider a body of mass m lying at rest on a smooth floor. Let a force F be applied on the body so that the body attains a velocity v after travelling a distance S (Figure 4).

Work done by the force on the body, W = FS                                                  …(i)
Since the velocity of the body changes from zero to v, so the body is accelerated. Let a be the acceleration of the body. Then according to Newton’s second law of motion.
F = ma
Substituting the value of F = ma in eqn.(î), we get
W = (ma)S

K.E of a body is direcdy proportional to

1. its mass and
2. square of its speed. SI unit of kinetic energy is joule (J). Kinetic energy of a body is said to be 1 joule, if a body of 1 kg mass moves with a speed of 1 ms^-2‘ Thus, 1 J = 1 kg m²s^-2.

Question 3.
Define kinetic energy of an object. Show that work done by a force on an object is equal to the change in kinetic energy of the object. (CBSE 2011)
Answer:
Definition : The energy possessed by a body by virtue of its motion is known as kinetic energy. In other words, we can say that anything which moves has kinetic energy.
Consider a body or an object of mass m moving with velocity u. Let a force F be applied on the body so that the velocity attained by the body after travelling a distance S is v (Figure 5).
Work done by the force on the body is given by
W =      FS                                                                               …(i)
Since velocity of the body changes so the body is accelerated. Let a be the acceleration of the body. Therefore, according to Newton’s second law of motion,
F =     ma                                                                             …(ii)
Using eqn. (ii) in eqn. (i), we get
Thus, work done by a force on a body is equal to the change in kinetic energy of the body This is known as work-energy theorem.

Question 4.
State the law of conservation of energy. Show that the energy of a freely falling body is conserved.
(CBSE 2011, 2012)

                                                                  Or

State and prove the law of conservation of energy for a freely falling body. (CBSE 2012)
Answer:
According to this law, “energy can neither be created nor be destroyed, but can be changed from one form to another form. ”

                                                                Or

When one form ofenergji is changed or transformed into other forms of energy, the total energy of an isolated system remains the same i. e., the total energy before transformation = the sum of the different energies transformed.
Consider a body of mass m at a height h above the ground. Suppose this position of the body is A (Figure 11).

Suppose the body at A is at rest i.e. v = 0.
At position A
Potential energy of the body, P.E. = mgh Kinetic energy of the body, K.E. = 0 Total energy (i.e., mechanical energy) of the body at A = P.E. + K.E. = mgh + 0 = mgh                                                       …(1)
Let the body falls freely under the action of gravity to position B through a height x. Now, the height of the body from the ground = (h-x)
At position B
Potential energy of the body, P.E. = mg (h – x)                                               ….(2)

∴ Total energy (i.e., mechanical energy) of the body at B= P.E. + K.E.
= mg (h – x) + mgx = mgh – mgx + mgx = mgh      …(5)
Finally, let the body touches the ground at C, so that the distance through which it falls = h.
At position C
Potential energy of body, P.E. = mg (0) = 0

∴ Total energy (i.e., mechanical energy) of the body at C = P.E. + K.E. = 0 + mgh = mgh      …(8)
From eqns. (1), (5) and (8), it is clear that the total energy (i.e., mechanical energy) of a body at any instant during free fall of the body remains constant. Hence, the law of conservation of energy is verified.

Question 5.
Show that when a body is dropped from a certain height, the sum of its kinetic and potential energy at any instant during its fall is constant. (CBSE 2011)
Answer:
Consider a body of mass m at a height h above the ground. Suppose this position of the body is A (Figure 11).

Suppose the body at A is at rest i.e. v = 0.
At position A
Potential energy of the body, P.E. = mgh Kinetic energy of the body, K.E. = 0 Total energy (i.e., mechanical energy) of the body at A = P.E. + K.E. = mgh + 0 = mgh                                                       …(1)
Let the body falls freely under the action of gravity to position B through a height x. Now, the height of the body from the ground = (h-x)
At position B
Potential energy of the body, P.E. = mg (h – x)                                               ….(2)

∴ Total energy (i.e., mechanical energy) of the body at B= P.E. + K.E.
= mg (h – x) + mgx = mgh – mgx + mgx = mgh      …(5)
Finally, let the body touches the ground at C, so that the distance through which it falls = h.
At position C
Potential energy of body, P.E. = mg (0) = 0

∴ Total energy (i.e., mechanical energy) of the body at C = P.E. + K.E. = 0 + mgh = mgh      …(8)
From eqns. (1), (5) and (8), it is clear that the total energy (i.e., mechanical energy) of a body at any instant during free fall of the body remains constant. Hence, the law of conservation of energy is verified.

Hope given Previous Year Question Papers for CBSE Class 9 Science Chapter 11 Work, Power and Energy are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.