CBSE Class 9

In this page, we are providing Natural Resources Class 9 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 9 Science Chapter 14 Natural Resources with Answers will help to score more marks in your CBSE Board Exams.

Class 9 Science Chapter 14 Extra Questions and Answers Natural Resources

Extra Questions for Class 9 Science Chapter 14 Natural Resources with Answers Solutions

Natural Resources Class 9 Extra Questions Very Short Answer Type

Question 1.
What are the resources available on Earth for life to exist?
Answer:
Air, water and land are the resources available on the Earth which help life to exist.

Question 2.
Name the compound of carbon responsible for the ozone hole in the atmosphere.
Answer:
Chlorofluorocarbons (CFC’s) are responsible for the ozone hole in the atmosphere.

Question 3.
State the temperature range on the surface of the moon.
Answer:
The temperature ranges from -190°C to 110°C on the moon

Question 4.
State any one difference between oxygen and ozone.
Answer:
Oxygen is a diatomic molecule with formula 02 whereas ozone is a triatomic molecule-with formula 0₃.

Question 5.
Name the stage in the life cycle of aquatic animals which is affected by a change in temperature.
Answer:
The stage of animals which is affected by the change in the temperature is – the eggs at the hatching stage, the larvae and the young ones of the animals.

Question 6.
Along with the natural resources available on the Earth, what else is required to meet the basic requirements of all life forms on the Earth?
Answer:
Solar energy is required to meet the basic requirements of all life forms on Earth.

Question 7.
How is biosphere a dynamic and stable system?
Answer:
There is a constant interaction between the biotic and the abiotic components of the global ecosystem (biosphere) which makes it a stable system. The basic composition and the structure of the system do not change while carrying out the various processes. So, it is a stable system.

Question 8.
How do forests play a major role in maintaining the water cycle?
Answer:
The amount of water vapour in the atmosphere is dependent on the transpiration of water from the leaves of the plants present in a forest. Also, the storage of water in watershed is influenced by the forests. So, forests play a major role in maintaining the water cycle.

Question 9.
Why is step farming done in hills?
Answer:
Step farming is done in hills to prevent soil erosion by slowing down the speed of the water running down the slopes.

Question 10.
Why are root nodules useful for plants?
Answer:
The root nodules of leguminous plants contain nitrogen-fixing bacteria like the Rhizobium which help to increase the fertility of the soil by fixing atmospheric nitrogen.

Question 11.
What are the biotic and the abiotic components of the biosphere?
Answer:

• Biotic component: comprises of living things.
• Abiotic component: comprises of non-living things like temperature, rainfall, air, water and soil.

Question 12.
What percentage of oxygen and nitrogen are present in the atmosphere?
Answer:
The approximate percentage of oxygen and nitrogen in the atmosphere are:
Oxygen: 21%, Nitrogen: 78%

Question 13.
Give the major source of minerals in the soil.
Answer:
The minerals in the soil depend upon the rocks from which the soil is formed. So, the rocks are the major source of minerals in the soil.

Question 14.
Name the two gases given out during the burning of fossil fuels which dissolve in rain to form acid rain.
Answer:
Sulphur dioxide and oxides of nitrogen.

Question 15.
Name the group of compounds responsible for ozone layer depletion.
Answer:
Chlorofluorocarbons (CFCs) are responsible for ozone layer depletion.

Natural Resources Class 9 Extra Questions Short Answer Type 1

Question 1.
What are the sources of oxygen in the atmosphere?
Answer:
The sources of oxygen in the atmosphere are:

• Oxygen released during photosynthesis by plants
• The dissociation of oxides from their compounds
• The disintegration of ozone in presence of UV rays
• As the water in combined form

Question 2.

1. What causes winds?
2. List any two methods of preventing soil erosion.

Answer:

1. Due to the unequal heating of land and water, the land get heated up faster during the day, the air on land rises up and creates a region of low pressure. As a result, the air over the sea moves towards the region of low pressure formed on the land. This causes winds to flow.

2. (a) Overgrazing by cattle should be avoided.
(b) Large scale afforestation should be done as roots of plants prevent the soil from getting carried away.
(c) Increasing the vegetation cover on the ground reduces the impact of flowing water on soil and prevents it from getting washed away.
(d) Contour farming can be done by ploughing the land in furrows across the natural slope of the land to trap water flowing down.
(e) Step farming is practised in hilly regions which reduce the flow of water and give it more time to percolate into the soil.

Question 3.
List the importance of oxygen gas and ozone gas in the atmosphere.
Answer:
Role of Oxygen gas: It helps in the process of combustion, respiration and formation of many organic compounds.
Role of Ozone: It absorbs the harmful UV rays of the Sun which can cause skin diseases and cancer on reaching the Earth’s surface.

Question 4.
Mention one method by which living organisms influence the formation of soil.
Answer:
The living organisms like lichens and mosses are the initial colonisers of rocks which secrete certain chemical substances that dissolve the minerals of rock and cause the gradual weathering of rocks. The rocks get broken down into small, fine particles of soil. So, living organisms play an important role in the formation of soil.

Question 5.
Explain the occurrence of land breeze in coastal areas.
Answer:
During the day, in coastal regions, the air above land gets heated faster and warm air being lighter rises up thereby creating a region of low pressure. The air over the sea then moves towards the area of low pressure. The movement of air from one region to the other creates winds. At night, water cools down slower than the land, so the air above water would be warmer than the air above land. This causes air over the land to move towards the region of low pressure over water.

Question 6.
What are the two ways in which carbon dioxide is fixed in the environment?
Answer:
Carbon dioxide is fixed in the atmosphere when:

1. Green plants utilise the carbon dioxide and convert it into glucose during photosynthesis.
2. Carbon dioxide dissolved in seawater in the form of carbonates gets used up by the marine animals for the formation of their shells.

Question 7.

1. Why do terrestrial forms require freshwater?
2. Give two examples where freshwater can be found in the frozen form on the Earth.

Answer:

1. The terrestrial organisms require freshwater as they face osmotic problems if kept in marine water because they have low osmotic concentration. In order to maintain the balance of the salts present in their body, freshwater organisms require a medium having less salt concentration i.e., freshwater.
2. Freshwater can be found in a frozen form at polar ice-caps and the glaciers.

Question 8.
What is the role of the atmosphere in climate control?
Answer:
The atmosphere acts as a buffer which checks excessive rise in temperature during the day and prevents excessive cooling of the Earth during the night. The atmosphere helps to keep the average temperature of the Earth steady.

Question 9.
State any two harmful effects of air pollution.
Answer:
The two harmful effects of air pollution are:

1. Respiratory problems and difficulty in breathing
2. Acid rains

Question 10.
1. Define the term ‘smog’.
2. Name any two types of disease caused by regularly breathing polluted air.
Answer:
1. Smog is a kind of air pollution, named for the mixture of smoke and fog in the air. The thick cloud of water droplets having smoke particles suspended in the atmosphere which restricts visibility is called smog.
2. Diseases caused by breathing polluted air are:
(a) Allergy
(b) Respiratory disorders
(c) Heart-related problems

Question 11.
Mention a cause and a consequence of acid rain.
Answer:
Cause of acid rain: The oxides of nitrogen and sulphur like nitrogen dioxide and sulphur dioxide released from the burning of fossil fuels gets mixed with water vapour present in the atmosphere to form acids. These acids dissolve in the rainwater and fall as acid rain on the Earth.

A consequence of acid rain:

1. The fertility of soil gets reduced due to the acidity created in the soil by the acid rains.
2. Acid rain corrodes the historic monuments and structures made of marble, metals, painted surfaces, etc.
3. The aquatic life is also harmed due to excess amount of acids which gets dissolved in water by acid rains.

Question 12.
What is meant by biogeochemical cycle? Name the two essentials which are transferred between different components of the biosphere.
Answer:
The movement of nutrient elements through the various components of an ecosystem i.e., biotic and the abiotic components, is called a biogeochemical cycle.
The two essentials which are transferred between different components of the biosphere are: Matter and energy,

Question 13.
What is the difference between nitrification and denitrification?
Answer:
Nitrification:
The process by which ammonia or ammonium compounds is converted into nitrites by Nitrosomonas and nitrites into nitrates by the Nitrobacter is called nitrification.

Denitrification:
The process by which the nitrites or nitrates are broken down into elemental nitrogen (N₂) by Pseudomonas or Thiobacillus is called denitrification.

Question 14.
Draw a well-labelled diagram to show the carbon cycle in nature.
Answer:

Question 15.
State the role of photosynthesis and respiration in the carbon cycle.
Answer:
Photosynthesis: Carbon dioxide in the atmosphere is fixed by green plants during the process of photosynthesis and converted into glucose.

Respiration: Glucose is oxidised during respiration to obtain energy. Carbon dioxide gets released during the process and is returned to the atmosphere. In this way photosynthesis and respiration help in maintaining the carbon cycle in nature.

Question 16.
Draw a neat labelled diagram to show the nitrogen cycle.

Question 17.
Name any four carbon-containing molecules which are essential for human beings.
Answer:
The carbon-containing molecules essential for human beings are:

1. Deoxyribonucleic acid-DNA
2. Proteins
3. Carbohydrates
4.  Fats

Question 18.
Draw a well-labelled diagram to show the oxygen cycle in nature.
Answer:

Question 19.
(a) Why do terrestrial forms require freshwater?
(b) Mention any two processes involved in the water cycle.
Answer:
(a) Terrestrial forms require water for carrying out the various cellular and metabolic process which occur in their body.
(b) Two processes involved in the water cycle are: Evaporation of water from water bodies and precipitation of water in the form of rain, hail or snow.

Question 20.
What is the importance of greenhouse gases present in the atmosphere?
Answer:
The greenhouse gases like carbon dioxide and methane prevent the escape of heat from the Earth. Thus, these gases play an important role of keeping the average temperature of the Earth constant.

Question 21.
What is the greenhouse effect? What will happen if the concentration of greenhouse gases increase in the air?
Answer:
The phenomenon in which the incoming sunlight is allowed to pass through the atmosphere but heat radiated back from the planet’s surface is trapped by the gases like carbon dioxide, water vapour and methane present in the atmosphere is called the greenhouse effect.

Increase in concentration of greenhouse gases would prevent the escape of heat from the Earth, increase the average temperature worldwide and result in global warming. Global warming will cause a rise in sea and odd climatic changes due to faster melting of glaciers and polar ice caps.

Natural Resources Class 9 Extra Questions Short Answer Type 2

Question 1.
1. The circulation of carbon is important in nature. Give reasons for your answer.
2. Explain any two processes involved in the cycling of nitrogen in the environment.
Answer:
1. The circulation of carbon dioxide is important in nature as it helps in maintaining the balance of carbon dioxide and oxygen in the atmosphere. Carbon dioxide is taken up by plants for photosynthesis and oxygen released during photosynthesis is utilised by the plants and animals for respiration.

Hence, it is necessary to maintain the balance of these gases. Carbon dioxide gas gets cycled between the atmosphere and the living organisms. An excess of carbon dioxide in the atmosphere causes global warming due to the greenhouse effect.

2. The two-process involved in the cycling of nitrogen in the environment are nitrogen fixation and ammonification.

(a) Nitrogen fixation in which the atmospheric nitrogen is converted into nitrites and nitrates which are water-soluble and are easily taken up the roots.

(b) Ammonification: Formation of ammonia due to the decomposition of dead organic matter is called as Ammonification.

Question 2.
State the reason for the following:
1. Excess burning of coal causes the greenhouse effect.
2. Soil is a mixture.
3. Temperature ranges from (-190°C -110°C) on the surface of the moon.
Answer:
1. Carbon dioxide gas is released during the burning of fuel like coal and petroleum. Carbon dioxide has a property due to which it allows rays of the Sun to pass through and reach the surface of the Earth but stops the long-wave infra-red radiations to pass through on being re-radiated from the surface of the Earth. Thus, carbon dioxide traps the heat rays of the Sun and causes the greenhouse effect.

2. Soil is a mixture of minerals, organic matter, gases, liquids, and the various organisms that together support life on Earth.

3. The moon does not have an atmosphere like that on the Earth which traps the heat rays of the Sun and keeps its warm. The atmosphere helps in checking rise in temperature during the day and the fall in temperature during night. So, in spite of being at the same distance from the Sun as the Earth, the temperature on moon ranges from (-190°C-110° C).

Question 3.
With the help of the diagram shows the carbon cycle in nature. What are the two ways in which carbon dioxide is fixed in the environment?
Answer:
The carbon cycle in nature can be depicted by the following diagram:

Carbon dioxide is fixed in the atmosphere by the following two ways:
1. Green plants utilise the carbon dioxide and convert it into glucose during photosynthesis.
2. Carbon dioxide dissolved in seawater in the form of carbonates gets used up by marine animals for the formation of their shells.

Question 4.
Sun as a natural factor helps in the formation of soil. Explain.
Answer:
The Sun helps in soil formation in the following ways:
Rocks expand when they get heated by the Sun during the day. During the night, the rocks cool down and contract. This results in the formation of cracks in the rocks as the rate of expansion and contraction are different. The rocks split and break into smaller pieces.

Question 5.
What is the percentage of oxygen in the atmosphere? Name any two compounds of oxygen found in nature. Name any three processes by which oxygen is used up in the atmosphere.
Answer:
The percentage of oxygen in the atmosphere is approximately 21%.
The diatomic form oxygen (O₂) and the triatomic form ozone (O₃) are the two forms in which oxygen is found in nature.
The three processes by which oxygen is used up in the atmosphere are:

• Combustion of fossil fuels.
• Respiration by living organisms.
• Decomposition of organic matter.
• Formation of oxides during fixation and other chemical reactions.

Question 6.
How is the greenhouse effect related to global warming? Explain.
Answer:
The phenomenon in which the incoming sunlight is allowed to pass through the atmosphere but heat radiated back from the planet’s surface is trapped by the gases like carbon dioxide, water vapour and methane present in the atmosphere is called the greenhouse effect.

An increase in the percentage of greenhouse gases like carbon dioxide and methane prevents the escape of heat from the Earth. So, the greenhouse effect is responsible for the increase in average temperature worldwide and is causing global warming. Global warming leads to melting of glaciers and polar ice caps at a faster rate which causes a rise of the sea and other odd climatic changes.

Question 7.
Why is water necessary for the living organisms?
Answer:
Water is necessary for living organisms because:

• All cellular metabolic processes occur in the water medium.
• The transportation of various substances from one part of the body to another occurs in dissolved form in water.
• All the reactions taking place in the cells or in our body occur between substances which are dissolved in water.

Question 8.
How are various biological factors needed for soil formation?
Or
Which symbiotic life forms can grow on stones and help in the formation of soil? Write the model of their action for making soil from rocks.
Answer:
Lichens are the symbiotic association of algae and fungi. Lichens help in the formation of soil. The living organisms like lichens and mosses are the initial colonisers of the rocks which secrete certain chemical substances which dissolve the minerals of rock and cause the gradual weathering of rocks. The rocks get broken down into small, fine particles of soil. So, biological factors play an important role in the formation of soil.

Question 9.
What is topsoil? Mention two factors that decide which plants will thrive on that soil.
Answer:
Topsoil refers to the topmost layer of the soil which contains humus, soil particles and living organisms.
The two factors that decide which plants will thrive on that soil are:

• The humus content and the type of microbes present in the soil.
• The size and texture of soil particles along with the composition of the soil.

Question 10.
What are the causes of soil erosion?
Answer:
The causes of soil erosion are:

1. Large scale deforestation
2. Large scale overgrazing
3. Industrialisation
4. Urbanisation
5. The land left uncultivated for a long time
6. Mining and other human activities which lead to loss of topsoil

Question 11.
Rivers from land, add minerals to seawater. Discuss how.
Answer:
Yes, it is true because water has the ability to dissolve a large number of substances. When the river water flows over the rocks containing soluble minerals, some of the minerals from the rocks get dissolved in the water. These minerals are carried away by the river water into the sea. Thus, the nutrients from the land are carried away by the river into the sea.

Question12.
How can we prevent the loss of topsoil?
Answer:
The loss of the topsoil can be prevented by the following ways:

1. Overgrazing by cattle should be avoided.
2. Large scale afforestation should be done as roots of the plants prevent the soil from getting carried away.
3. Increasing the vegetation cover on the ground reduces the impact of flowing water on soil and prevents it from getting washed away.
4. Contour farming can be done by ploughing the land in furrows across the natural slope of the land to trap water flowing down.
5. Step farming is practised in hilly regions which reduces the flow of water and gives it more time to percolate into the soil.

Question 13.
How is the life of organisms living in water affected when water gets polluted?
Answer:
When the water gets polluted, the life of organisms living in water gets affected in the following ways:

1. The domestic wastewater contains detergents and nutrients which increase the growth of aquatic plants, algae, etc., and reduces the amount of dissolved oxygen in the water body. This adversely affects the aquatic animals as they die due to scarcity of oxygen.
2. The fertilisers, pesticides, etc., which get washed into the water body from the agricultural fields also harm the aquatic organisms.
3. Many disease-causing organisms are also released in the domestic wastewater which acts as a source of many water-borne diseases like cholera.
4. The heated water released directly into the water bodies by some industries can cause the death of aquatic organisms which are not able to tolerate the sudden change in temperature.
5. The heavy metals dissolved in polluted water is also harmful to the living organisms.

Question 14.
During summer, if you go near the lake, you feel relief from the heat, why?
Answer:
We feel relief from the heat when we go near a lake during summer because:
1. The Sunrays heat the land near the lakes more quickly than the water of the lake. The hot air rises up to create a region of low pressure on the land. Evaporation of the water causes cooling of the air above the lake and this cool air flows from the lake towards the region of low pressure on the land. The cool air gives relief to us from the heat.

Question 15.
In the coastal area, wind current moves from the sea towards the land during the day; but during the night
Answer:
During the day, in the coastal regions, the air above the land gets heated faster and the warm air being lighter rises up thereby creating a region of low pressure. The air over the sea then moves towards the area of low pressure. The movement of air from one region to the other creates winds. At night, water cools down slower than the land, so the air above the water would be warmer than the air above land. This causes air over the land to move towards the region of low pressure over water.

Question 16.
Following are a few organisms
(a) lichen
(b) mosses
(c) mango tree
(d) cactus.
Which among the above can grow on stones; and also help in the formation of soil? Write the model of their action for making soil.
Answer:
Lichens and the mosses can grow on stones and help in the formation of soil. The chemical substances secreted by the living organisms like lichens and mosses degrade the rocks and convert them into fine particles of soil. They also cause crevices and cracks in the rocks which help in the colonisation of rocks by bigger plants. The roots of these plants widen the cracks and cause the breakdown of large rocks.

Question 17.
Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?
Answer:
The abiotic factors involved in soil formation are: Sun, water, wind.
The biotic factors involved in soil formation are: lichens, mosses and trees, microorganisms, etc.

Question 18.
All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.
Answer:
Elements like C, N, S, P, H and O enter the living forms through the process of photosynthesis and on getting absorbed from soil by the plants and living organisms.

Question 19.
Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
Answer:
The biotic and the abiotic components of the biosphere interact with each other and continuously cycle the elements like nitrogen, oxygen and carbon through their respective cycles called as biogeochemical cycles. This helps to maintain the percentage of these gases almost constant in the atmosphere.

Question 20.
Why does the moon have very cold and very hot temperature variations e.g., from -190°C to 110°C even though it is at the same distance from the Sun as the Earth is?
Answer:
The moon does not have an atmosphere due to which very cold and very hot temperature variations from -190°C to 110°C occur on its surface. The atmosphere helps in maintaining the temperature as it prevents the excessive rise in temperature during daytime and prevents excessive cooling during the night by trapping heat energy of the Sun.

Question 21.
Why do people love to fly kites near the seashore?
Answer:
The wind blows from the sea towards the land during the daytime which helps in flying the kite higher. Also, the wind coming from the sea is cooler which makes the kite flyers feel comfortable. So, people love to fly kites near the seashore.

Question 22.
Why does Mathura refinery pose problems to the Taj Mahal?
Answer:
The harmful gases like sulphur dioxide released from the Mathura oil refinery get mixed with the water vapour present in the air and form acids like sulphuric acid. This acid falls along with the rains in the form of acid rain. The acid present in the acid rain is causing the corrosion of the marble used in the Taj Mahal. The colour (yellowing of marble was caused), as well as the quality of the marble, was getting degraded due to the acid rains. Thus, Mathura refinery posed a problem to the Taj Mahal.

Question 23.
Why do lichens not occur in Delhi whereas they commonly grow in Manali or Darjeeling?
Answer:
Lichens are bio-indicators as they help in assessing the level of pollution in the environment. They are highly sensitive to the gaseous pollutants like sulphur dioxide released from the vehicles and other sources. Delhi has a large number of vehicles and the industries which emit these gases compared to Manali or Darjeeling. So, lichens are unable to grow in Delhi.

Question 24.
Why does water need conservation even though large oceans surround the landmasses?
Answer:
The freshwater resources like river, ponds, lake, etc., are not evenly distributed on the Earth. Most part of the Earth is covered by the oceans and seas which have marine water (salty water) which is not fit for human consumption. So, there is a need to conserve the freshwater resources and the water available to us.

Question 25.
There is a mass mortality of fishes in a pond. What may be the reasons?
Answer:
The mass mortality of fishes in a pond can be the result of one or more of the following factors:

1. Thermal pollution due to the heated water directly released into the water body which harms the organisms that are not able to withstand the sudden change in temperature.
2. The release of heavy metals, poisonous substances like mercury or other harmful chemicals into the waterbody.
3. Blockage of the gills of the fishes by the pollutants or the suspended particles released into the waterbody.
4. Harmful pesticides or chemicals washed into the waterbody from the agricultural fields.
5. Toxic wastes released into the water by the industries.

Question 26.
Lichens are called pioneer colonisers of bare rock. How can they help in the formation of soil?
Answer:
The chemicals released by the lichen cause the gradual weathering of the large particles of rock into smaller fine particles of soil. Thus, they help in the formation of soil.

Question 27.
“Soil is formed by water.” If you agree to this statement then give reasons.
Answer:
Yes, water helps in the formation of soil as it helps in the breakdown of large rocks into fine particles of soil by the following two ways:

1. The water enters the cracks and crevices in the rocks, gets unevenly heated by the Sun and when it expands during freezing in the winter season, the rocks break down in smaller pieces.
2. Also, the fast running water over the surface of the rocks causes weathering of rocks to form soil.

Question 28.
Fertile soil has lots of humus. Why?
Answer:
Fertile soil has a lot of hummus because

1. Soil particles are bound in the form of crumbs by the humus which helps the soil in aeration as well as hydration.
2. Humus contains many kinds of minerals dissolved in it.
3. Growth of the plants is enhanced by the various chemicals present in humus.
4. Soil becomes porous due to humus which facilitates the penetration of roots into the soil.

Question 29.
Why is step farming common in hills?
Answer:
Step farming is practised in hilly regions which reduce the flow of water or the rainwater and gives it more time to percolate into the soil.

Question 30.
Why are root nodules useful for the plants?
Answer:
The plants called legumes to harbour the nitrogen-fixing bacteria like Rhizobium in their roots in the form of root nodules. These bacteria convert the atmospheric nitrogen into nitrites or nitrates which can be assimilated by plants.

Natural Resources Class 9 Extra Questions Long Answer Type

Question 1.
1. Make a neat and labelled sketch of the nitrogen cycle in nature.
2. Describe in brief the role of nitrogen-fixing bacteria and lightning in fixing nitrogen.
Answer:
1. The nitrogen cycle is:

2. The atmospheric nitrogen can be fixed in the following ways:
By nitrogen-fixing bacteria: The nitrogen-fixing bacteria live either in a symbiotic association like the Rhizobium in the root nodules of the legumes or live freely like Azotobacter. The bacteria fix the atmospheric nitrogen into nitrates which are absorbed by the plants in soluble form and assimilated in their body.

By lightning: Lightning has enormous energy which breaks nitrogen molecules and enables their atoms to combine with oxygen present in the air to form nitrogen oxides. These oxides dissolve in rain, form nitrates and are carried to the Earth with the rains.

Question 2.
Explain the role of the atmosphere as a blanket. List the factors deciding the rainfall patterns.
Answer:
The atmosphere is a blanket of air around the Earth which acts as a buffer to prevent the excessive or
sudden rise of temperature during the day and also prevents excessive cooling of the Earth during the night. It slows down the escape of heat into the outer space during the night.

Thus, the atmosphere helps to keep the average temperature of the Earth fairly steady during the day and also during the whole year. The prevailing wind patterns decide the rainfall patterns. The South-West monsoon and the North-East monsoon cause rains in large parts of India.

Question 3.
1. Many municipal corporations are trying water harvesting to improve the availability of water. Give reason.
2. Rainwater sometimes contains traces of acid. Why? Explain in brief.
Answer:
1. The Municipal Corporations are trying water harvesting in order to recharge the underground water reservoirs and the underground water level. This ensures the availability of water during the scarcity of rainfall or water. Rainwater harvesting involves the collection of water from surfaces on which rain falls and stores this water for later use. Generally, the water is collected from the roofs of buildings and stored in rainwater tanks.

2. Combustion of fossil fuels releases oxides of nitrogen (NO₂) and sulphur (SO₂) which dissolve in rainwater to form their respective acids. These acids then fall along with rains and such rain is called acid rain. Due to the presence of such acids, the rainwater sometimes contains traces of acids.

Question 4.
How does the addition of undesirable substances and change in temperature affect water life?
Answer:
Addition of undesirable substances affects the water life in the following ways:

1. Addition of harmful chemicals or metals like mercury, lead, etc., cause poisoning of water bodies and harm aquatic organisms.
2. The pathogens released into the water bodies are the cause of many human diseases like cholera, typhoid, etc.
3. Aquatic organisms are harmed and even killed due to deficiency of oxygen which occurs when the addition of sewage, fertilisers and nutrients in the water body resulting in excessive growth of algae. The algae drain out the oxygen from the water body.

The change in temperature can also affect water life because:

1. The variation in temperature affects the breeding patterns of aquatic animals.
2. The hatching of the eggs is adversely affected due to the changes in the temperature of the water.

Question 5.
What are the various factors or the processes that make soil?
Answer:
Soil is formed due to various physical, chemical and biological processes which result in the breakdown of rocks into fine particles of soil over millions of years. The formation of soil occurs due to factors and processes like Sun, water, wind, living organisms and lichens.

1. Sun: Rocks expand when they get heated by the Sun during the day. During the night, the rocks cool down and contract. This result in the formation of cracks in the rocks as the rate of expansion and contraction are different. The rocks split and break into smaller pieces.

2. Water: Water acts in two ways to break the large rocks into small pieces. Water enters the cracks and crevices in the rocks, gets unevenly heated by the Sun and when it expands during freezing in the winter season, the rocks break down into smaller pieces. Also, the fast running water over the surface of the rocks causes weathering of rocks to form soil.

3. Wind: The winds carry small rocks and sand from one place to another and these strong winds rub against the large rocks to erode them.

4. Living organisms (Lichens): The chemical substances secreted by the living organisms like lichens degrade the rocks and convert them into fine particles of soil.

Question 6.
How do fossil fuels cause air pollution?
Answer:
Fossil fuels like coal and petroleum produce oxides of nitrogen and sulphur on combustion. These gases react with water vapour present in the air to form acids which fall down along with rains on the Earth. Acid rain is very harmful to the plants, animals and the microorganisms present in the soil. Also, the suspended particulate matter released on the burning of fossil fuels cause respiratory problems to human beings and reduces visibility when it forms smog.

Question 7.
What are the causes of water pollution? Discuss how you can contribute in reducing water pollution. Ans. Addition of undesirable and harmful substances in water or the removal of useful substances from water
is referred to as water pollution. It is caused due to:

1. Addition of fertilisers and pesticides washed away from the agricultural field into the nearby water bodies.
2. Disposal of domestic sewage into the waterbody like rivers.
3. The death of many aquatic organisms occurs when hot water from the industries is directly released into the water body. This also reduces the amount of dissolved oxygen in the waterbody.
4.  Washing of the clothes in the waterbody using detergents.
5. Many harmful radioactive substances released from the industries dumped into the waterbody.

Water pollution can be reduced by the following measures:

1. The sewer lines should not be directly connected to the waterbody.
2. Disposal of garbage and wastes into the waterbody should not be allowed.
3. Toxic compounds released from the industries should not be dumped in the water bodies.
4. Detergents increase the nutrient content of water which is harmful to aquatic organisms as the amount of dissolved oxygen gets reduced in water due to excessive algal growth. Therefore water containing detergents should not be allowed to run off into water bodies.
5. Trees should be planted near the banks of the river to prevent soil erosion which leads to siltation in the water bodies.

Question 8.
A motor car, with its glass totally closed, is parked directly under the Sun. The inside temperature of the car rises very high. Explain why.
Answer:
Glass has a property due to which it allows the radiations of the Sun to pass through and enter the car. Infrared radiations also enter the car along with other radiations. Glass is transparent to infrared. radiation from the Sun having smaller wavelength but opaque to longer wavelength radiations that are emitted by the interior of the car.

The infrared radiations get re-radiated by upholstery and other inner parts of the car but cannot pass out of the glass like the other radiations. So, the heat trapped inside raises the temperature inside the car.

Question 9.
Justify “Dust is a pollutant”.
Answer:
Dust can be considered as a pollutant because:

1. Suspended particles are present in the dust which can enter the respiratory systems of the organisms and can cause asthma, bronchitis, allergies or other respiratory diseases.
2. When dust falls on the leaf surface, it can cause blocking of the stomata which adversely affects the process of photosynthesis and plant growth.
3. Many heavy metals and toxic compounds are present in the dust which can harm living organisms.
4. Dust can be harmful to the eyes of the organism as irritation and reddening of eyes can be caused due to it.

Question 10.
Explain the role of the Sun in the formation of soil.
Answer:
The Sun helps in soil formation in the following ways:
Rocks expand when they get heated by the Sun during the day. During the night, the rocks cool down and contract. This result in the formation of cracks in the rocks as the rate of expansion and contraction are different. The rocks split and break into smaller pieces.

Question 11.
Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Answer:
Carbon dioxide is necessary for the plants, as it is utilised during the process of photosynthesis. It acts as a raw material for photosynthesis and helps in maintaining the temperature on the Earth. If the concentration of carbon dioxide increases in the atmosphere above a certain level, it traps more heat of the Sun because it is a greenhouse gas.

This ultimately results in an increase in the average temperature on Earth and causes global warming. Due to higher temperatures, the polar ice caps, glaciers and the snow of mountains melt faster. This can lead to floods and an increase in seawater level. So, carbon dioxide is considered a pollutant.

Natural Resources Class 9 Extra Questions HOTS

Question 1.
What is the fate of the glucose molecules formed in photosynthesis?
Answer:
The glucose molecules formed during photosynthesis are either stored in the form of starch in the green plants or get transported in the form of sucrose to the various parts of the plant. Glucose is also utilised by the plants during respiration to obtain energy.

Question 2.
What is the likely outcome if all the oxygen in the environment gets converted into ozone?
Answer:
If all the oxygen in the environment gets converted into ozone it will be harmful to the living organisms as ozone adversely affects the living organisms and would eventually kill them.

Question 3.
We are lucky that ozone is not stable near the Earth’s surface. Why?
Answer:
The ozone present in the lower atmosphere is called ‘bad ozone’ as it adversely affects the living organisms, corrodes metals, acts as a greenhouse gas and creates respiratory problems in animals. So, we are lucky that ozone is not stable near the Earth’s surface as it gets converted into oxygen or the various oxides.

Question 4.
1. Nitrogen-fixing bacteria are usually found only in the root nodules of leguminous plants. Why?
2. Name a non-leguminous plant which has nitrogen-fixing bacteria in root nodules and the microbe present in it.
Answer:
1. The nitrogen-fixing bacteria are usually found only in the leguminous plants as the roots of the leguminous plants provide shelter and the specific conditions required for such bacteria. The bacteria like Rhizobium live in symbiotic association with the roots of leguminous plants.

2.  Alnus is a non-leguminous plant which has a nitrogen-fixing bacteria called Frankia in its root nodules.

Question 5.
What will be the consequences if all the decomposers are removed from the Earth?
Answer:
Decomposers play a vital role in the recycling of various nutrients. The recycling of the nutrients would be hindered in the absence of decomposers. They also help in the decomposition of dead plants, animals and organic matter. In the absence of decomposers, the Earth would get covered by the remains of such organisms and it would become difficult for the organisms to survive on Earth.

Question 6.
Excessive use of pesticides in the fields can adversely affect the fishes living in the nearby ponds. How?
Answer:

• The pesticides used in the fields can get washed into the nearby water bodies by the rains and flowing water.
• These pesticides cause a phenomenon called biological magnification which adversely affects the fishes of the pond.

Question 7.
Excess use of fertilisers in the field is not advisable to the farmers. Give reasons.
Answer:
Excess use of fertilisers increases the food production for a short term but in the long term, it is not advisable to the farmers because
1. Excess use of fertilisers increases the salinity of the soil and reduces its fertility.
2. The fertilisers can get washed away into the nearby ponds where they cause excessive growth of algae due to nutrient enrichment. This depletes the dissolved oxygen from the water body and harms the other aquatic organisms.

Question 8.
The public transport like buses and the autos have shifted to CNG instead of petrol or diesel in Delhi. Why?
Answer:
The public transport like the buses and the autos have shifted to CNG instead of petrol or diesel in Delhi because the gases released from these vehicles cause a lot of pollution and harms the environment in following ways:

• The oxides of nitrogen and sulphur released from the vehicles result in acid rains which is harmful to the living organisms.
• The harmful gases from the exhaust result in several problems like asthma, respiratory disorders, cancer, etc.

Question 9.
Discharge of sewage into the water body decreases the amount of oxygen dissolved in water. How?
Answer:
The sewage water consists of a lot of organic matter which is decomposed by the microorganisms present in the water body. The microorganisms multiply at a rapid rate and consume a lot of dissolved oxygen in order to decompose the organic matter. This reduces the amount of dissolved oxygen in the water.

Question 10.
What will be the result if all the plants get eliminated from the Earth?
Answer:
Plants perform photosynthesis and release oxygen during the process which is used by the other organisms for survival. If all the plants become extinct, eventually all the oxygen requiring living organisms including us will get eliminated from the Earth.

Natural Resources Class 9 Extra Questions Value Based (VBQs)

Question 1.
Vijay is the son of a rich businessman. He lives in a very big house. He always insists and reminds the family members to switch off lights, fans, TVs, etc., of rooms when there is no one in the room, so that use of electricity is minimum. He realises that power generation on a large scale in thermal power plants produces a lot of carbon dioxide and fly ash.
Read the given passage and answer the following questions:

1. How is carbon dioxide responsible for global warming?
2. What measures will you take to reduce levels of carbon dioxide?
3. What values are displayed by Vijay in his action and thoughts?

Answer:
1. Carbon dioxide has a property due to which it allows rays of Sun to pass through and reach the surface of the Earth but stops the rays from being re-radiated from the surface of Earth. The heat of the Sun rays gets trapped by carbon dioxide in this way and causes global warming.
2. The levels of carbon dioxide can be reduced in the atmosphere by increasing the efficiency of engines of vehicles, large scale afforestation, reducing the emission of carbon dioxide from the industries and using alternative sources of energy in place of fossil fuels.
3. The values shown by Vijay are a concern for the environment, intelligence, awareness and scientific attitude.

Question 2.
Due to the establishment of a petroleum refinery near the city, many people started suffering from respiratory problems and the marble used in their houses turned yellow. A survey carried out by Arpit and his colleagues attributed this to the gases released from the refinery. They consulted the Government agencies and suggested to shift the refinery away from the city.
Based on the above, answer the following questions:

1. What can be the reason behind the yellowing of marble?
2. What are the various harmful effects of air pollution?
3. What values are depicted by the efforts of Arpit and his colleagues?

Answer:

1. The oxides of nitrogen and sulphur released from the petroleum refinery dissolve in rainwater to form acids and fall on the Earth. When this acid rain falls on marble it causes yellowing of the marble.
2. The other harmful effects of air pollution are:
   (a) Formation of smog which harms living organisms.
   (b) Respiratory problems, bronchitis, asthma, cancer, etc.
3. The values depicted by Arpit and his colleagues are scientific aptitude, care for the environment and a responsible citizen.

Question 3.
Amrita saw that the farmers of her village use excessive fertilisers and pesticides on their crop. She searched the internet for the effect of such action on the environment. She came to know that their excessive use is harmful to the environment. She talked to the Head of the village and the farmers were motivated to use fertilisers and pesticides judiciously. They were also motivated to practice organic farming for better crop yield.
Based on the above, answer the following questions:
1. How is excessive use of fertilisers and pesticides harmful to the environment?
2. What is organic farming?
3. What values are shown by Amrita in solving the problem?
Answer:
1. The fertilisers and the pesticides get washed away into the nearby water bodies with rainwater or the flowing water.
Excess use of fertilisers causes uncontrolled growth of algae in water bodies which depletes the dissolved oxygen in the water and causes death other aquatic organisms. Excess use of pesticides causes biological magnification which leads to death of many fishes in the water bodies.
2. Organic farming is a method of crop production in which no chemical pesticides or fertilisers are used during the cultivation of crops.
3. The values shown by Amrita are curiosity, inquisitive nature, care for the environment and scientific attitude.

Question 4.
Zeenat and her sister were very happy when their father brought home a new refrigerator. She saw a sticker pasted on the refrigerator which read ‘CFC free’. She asked her father about it. Her father told her that the compounds called CFC are the cause of the ozone hole and so they are not used in the refrigerators to save our environment.
Read the above passage and answer the following:

1.  What is ozone and why is it important?
2. What are CFCs and why are they harmful?
3. What values are shown by Zeenat and her father?

Answer:

1. Ozone is a triatomic molecule of oxygen with formula 03. It traps the harmful rays of the Sun and protects the living organisms.
2. The CFCs are the carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process. They persist in the atmosphere and degrade the ozone layer.
3. The quality shown by Zeenat is a curious nature. Her father shows the values of concern for the environment, patience and imparting right knowledge to children.

Question 5.
A farmer came for a consultation with Rajni who worked as ‘Kisan Mitra’ in the village. He told her that he was growing leguminous crop in the field, so what will by the right amount of nitrogenous fertilisers required in his field? Rajni told him that since he was growing leguminous crops in the field, he does not require adding more nitrogenous fertilisers in the field. She further suggested him to grow the leguminous crop alternately with maize or wheat.
Based on the above, answer the following questions:
1. Why did Rajni advise the farmer not to add more nitrogenous fertilisers in his field?
2. Why did she suggest him to grow leguminous crop alternately with maize or wheat?
3. What values are shown by Rajni?
Answer:
1. Rajni advised the farmer not to add more nitrogenous fertilisers as the leguminous plants which the farmer had sown in the field have root nodules which contain nitrogen-fixing bacteria. These nitrogen-fixing bacteria fix the atmospheric nitrogen and give it to the plant, so no additional nitrogen-containing fertilisers are required in the field.

2. Rajni advised the farmer to grow leguminous crop alternately with maize or wheat as the nutrients are taken up by the wheat or maize from the soil will be restored by the nitrogen-fixing bacteria present in the root nodules of the leguminous crop. In this way, the fertility of the soil will be restored and enriched again by the leguminous crop. The process is called crop rotation.

3. The values shown by Rajni are patience, knowledge, proper decision making, scientific aptitude, concern for the environment

In this page, we are providing Why Do we Fall Ill Class 9 Extra Questions and Answers Science Chapter 13 pdf download. NCERT Extra Questions for Class 9 Science Chapter 13 Why Do we Fall Ill with Answers will help to score more marks in your CBSE Board Exams.

Class 9 Science Chapter 13 Extra Questions and Answers Why Do we Fall Ill

Extra Questions for Class 9 Science Chapter 13 Why Do we Fall Ill with Answers Solutions

Why Do we Fall Ill Class 9 Extra Questions Very Short Answer Type

Question 1.
What are infectious or communicable diseases?
Answer:
The diseases which are caused by infectious agents are called as infectious diseases as they can spread from one person to another through some medium or by direct contact.
Example: Pneumonia, common cold, tuberculosis, etc.

Question 2.
What are congenital diseases?
Answer:
The diseases which are present in a person since birth are called congenital diseases.
Example: colour blindness.

Question 3.
Give one local and one general effect of the inflammation process.
Answer:
Swelling or pain is a local effect. Fever or headache is a general effect.

Question 4.
Name the organism causing the following diseases:
(a) Kala-azar
(b) Sleeping sickness
Answer:
Kala-azar is caused by Leishmania; Sleeping sickness is caused by Trypanosoma.

Question 5.
It was diagnosed that a patient has lost the power of fighting any infection.
(i) Name the disease the patient is suffering from.
(ii) Name the pathogen responsible for the disease.
Answer:
(i) AIDS.
(iii) HIV is the causative organism of AIDS. [HIV-Human immunodeficiency virus]

Question 6.
What is immunity?
Answer:
The ability of the body of a person to fight against the disease causing organisms is called immunity. Name any disease that can be prevented by using vaccines.

Question 7.
The diseases which can be prevented by using vaccines.
Answer:
The diseases which can be prevented by using vaccines are polio, small pox, diphtheria, tetanus, measles, etc.

Question 8.
What are principles of treatment of a disease?
Answer:
The principles of treatment are:

• reducing the effects of the disease.
• to kill the cause of the disease.

Question 9.
How do children in many parts of India get immune to hepatitis-A by the time they are five year old?
Answer:
The children become immune to hepatitis A virus as they are exposed to hepatitis A virus present in the water they drink.

Question 10.
Name the causative organisms of tuberculosis and cholera.
Answer:
Tuberculosis: Caused by bacterium called as Mycobacterium tuberculosis.
Cholera is caused by a bacterium called as Vibrio cholera

Why Do we Fall Ill Class 9 Extra Questions Short Answer Type 1

Question 1.
What are the differences between acute and chronic diseases?
Answer:
Acute disease:

• The disease which lasts for only very short periods of time is called acute disease.
• They get over soon and do not get much time to affect the health more adversely. Example: Common cold

Chronic disease:

• The disease which can last for a long time, even as much as a lifetime is called chronic disease.
• They have a long-term effect on the health of a person. Example: Elephantiasis

Question 2.
What is a pandemic disease? Give one example.
Answer:
The disease which affects the health of human population all over the world is called a pandemic disease. For example, AIDS.

Question 3.
Mention the symptoms because of which you will visit a doctor and why?
Answer:
High fever, headache, tiredness, loose motion, cough and cold, loss of appetite and body weight are some of the symptoms for which we will visit a doctor because the doctor would be able to ascertain the disease caused on the basis of the symptoms produced and give medication accordingly.

Question 4.
Why is DPT called triple antigen?
Answer:
DPT is called as triple antigen as it affects three antigens to produce the antibodies against them. The diseases are: Diphtheria, Pertussis and Tetanus.

Question 5.
What are the symptoms shown by a person if the
(i) lungs get infected?
(ii) stomach is infected?
Answer:
(i) Cough, breathlessness, tiredness are the symptoms produced if the lungs of a person get affected by a disease.

(ii) Loose motion, vomiting and stomachache are the symptoms produced when the stomach of a person gets affected by a disease.

Question 6.
“In our country majority of children are already immune to hepatitis A without giving its vaccine to them.” Justify this statement giving reasons.
Answer:
Majority of the children are already exposed to the hepatitis A virus by the time they are five years old because the water which the children generally drink contains the hepatitis A virus. The immune system thus helps to develop immunity against the virus.

Question 7.
List any four factors that must be taken care of by an individual for keeping good health.
Answer:
The four factors which must be taken care by an individual for keeping good health are:

• Proper nourishing balanced diet
• Clean and hygienic environment
• Good social environment
• Proper sanitation and cleanliness

Question 8.
Why are antibiotics effective against bacteria?
Answer:
Antibiotics block the biochemical pathways of the bacteria which inhibit their growth and kill them. For example: Penicillin blocks the pathway involved in the synthesis of cell wall which protects the bacteria. This inhibits their growth and kills them.

Question 9.
Influenza or common cold spreads faster and is difficult to control. Explain.
Answer:
Influenza and common cold are infectious diseases which are spread through air, so it becomes difficult to control them.

Question 10.
Why are overcrowded and poorly ventilated areas, major factors in the spread of air-borne diseases?
Answer:
In poorly ventilated and overcrowded areas, the little droplets containing air-borne microbes thrown by an infected person on coughing or sneezing, can be easily inhaled by a healthy person standing close by. This can start a new infection in the healthy person. Hence, such areas are major factors in the spread of air-borne diseases.

Question 11.
(a) Name the organ into which the malarial parasite enters after a mosquito bite.
(b) Give two examples of air-borne diseases.
Answer:
(a) The malarial parasite enters the liver of the healthy person after mosquito bite.
(b) Common cold and pneumonia are some air-borne diseases.

Question 12.
What are non-infectious diseases? Give two examples of non-infectious diseases.
Answer:
The diseases which do not spread from one person to the other person in the community are called as non-infectious diseases. They are caused due to internal factors.
Example: Cancer, high blood pressure, diabetes, etc.

Question 13.
Identify infectious and non-infectious diseases from the diseases given below: Tuberculosis, goitre, marasmus and typhoid.
Answer:

• Infectious diseases are tuberculosis and typhoid.
• Non-infectious diseases are goitre and marasmus.

Question 14.
Write the symptoms and diseases associated with the following:
(a) when microbes attack the lungs
(b) when the virus enters the liver
Answer:
(a) Tuberculosis may occur when microbes attack the lungs. The symptoms would be persistent cough, blood in sputum, prolonged low fever.

(b) Jaundice may occur when the virus enters the liver. The symptoms would be headache, high fever, loss of appetite and dark yellow coloured urine.

Question 15.
Why does a person suffering from the disease HIV-AIDS dies even due to small infection?
Answer:
The HIV damages the immune system of the person suffering from AIDS. Due to this the body of the person is unable to fight against even the small infections. The immune system of the person becomes very weak and ultimately leads to the death of the person due to several infections.

Why Do we Fall Ill Class 9 Extra Questions Short Answer Type 2

Question 1.
(a) Define disease.
(b) Explain briefly the two groups of diseases.
Or
Differentiate between infectious and non-infectious diseases.
Answer:
(a) Disease refers to any condition that disturbs the normal functioning of the living organism. It is a condition of disturbed ease when an individual feels uncomfortable.

(b) The two groups of diseases are infectious diseases and the non-infectious diseases.
Infectious diseases:

• These diseases are caused by infectious agents. These can spread from one person to another through some medium or by direct contact.
• Example: Pneumonia, common cold, tuberculosis, etc.

Non-infectious diseases:

• These do not spread form one person to the other person in the community. They are caused due to
• internal factors.
  Example: Cancer, high blood pressure, diabetes, etc.

Question 2.
What are acute and chronic diseases? Which one of the two is more harmful and why? Give an example in support of your answer.
Answer:
Acute disease:

• The disease which lasts for only very short periods of time is called acute disease.
• They get over soon and do not get much time to affect the health more adversely. Example: Common cold

Chronic disease:

• The disease which can last for a long time, even as much as a lifetime is called chronic disease.
• They have a long-term effect on the health of a person. Example: Elephantiasis

Chronic diseases are more harmful as they persist for a long time and thus adversely affect the general health of the person suffering from them.

Question 3.
Giving reasons, justify that it is difficult to prepare antiviral medicines than antibiotics.
Or
Why is it difficult to prepare anti-viral medicines than antibiotics?
Or
Explain why antibiotics do not work against viruses but work against many group of bacteria.
Answer:
Antibiotics are the chemicals which usually block the biochemical pathways of the bacteria. This inhibits their growth and kills them. But, the viruses do not have their own biochemical pathways as present in the bacteria. Viruses use the host machinery to multiply themselves. So, it becomes difficult to prepare anti-viral vaccines in order to inhibit their growth.

Question 4.
How do diseases spread through air? Name two such diseases.
Answer:
The diseases spread through air when little droplets thrown out by an infected person who sneezes or coughs are inhaled by a healthy person. This results in a new infection in the healthy person.
Example: Common cold, pneumonia and tuberculosis.

Question 5.
Why does a person who has suffered once from small pox cannot suffer with it again?
Answer:
The immune system of our body responds against the disease causing small pox virus when it encounters it for the first time. This interaction is slower and less vigorous, but the immune system remembers the virus specifically. Whenever the immune system encounters the virus after this first response, the interaction is more vigorous and the immune system completely eliminates the virus. Thus, the small pox virus is not able to affect the person who has suffered from it once.

Question 6.
How is the principle of immunisation implemented for eliminating polio?
Answer:
The polio vaccine which is administered to the children in the form of polio drops contains the weakened polio causing pathogen which is not able to cause the disease but enables the immune system of the child to produce antibodies against the polio virus. Subsequent encounter of the child to the polio virus activates the immune system which kills the polio virus and protects the immunised child from the disease. Thus, principle of immunisation helps in eliminating polio.

Question 7.
Give the cause and the remedy of:
(a) Hepatitis
(b) AIDS
(c) Malaria
Answer:

Question 8.
“Being disease free is not the same as being healthy.” Explain the statement by giving an example.
Answer:
Disease refers to any condition that disturbs the normal functioning of the living organism. It is a condition of disturbed ease when an individual feels uncomfortable. Being disease-free is a concept which applies to individual sufferer.

Even a disease free person can be considered as having a poor health if the person is unfit in terms of social and mental health. So, health is a concept which applies to societies and communities.

For example: a disease free person suffering from mental stress and tension cannot be considered as healthy.

Question 9.
A person was bitten by a stray dog. After some days his nature gets irritated, he started fearing water.
(a) Name the disease.
(b) Is there any vaccine available?
(c) Is there any plan of your local authority for the control of this disease?
Answer:
(a) The disease caused due to bite of a stray dog is rabies.
(b) Yes, anti-rabies vaccine is available.
(c) Local authorities have planned immunisation of the stray dogs against the disease.

Question 10.
It was diagnosed that the body of a patient had lost his power of fighting any infection. Name the disease the patient was suffering from. Which microbe is responsible for this disease? Give two ways by which it spreads from one person to another.
Answer:
The disease is called AIDS (Acquired immunodeficiency syndrome) and the microbe which is responsible for the disease is a virus called HIV (Human immunodeficiency virus). The ways to control the disease are:

• Creating awareness among people regarding the modes of spread of the disease.
• Use of disposable syringes in hospitals and clinics.
• Avoiding sexual contact with multiple partners.

Question 11.
Give two examples for each of the following:
(a) Acute diseases
(b) Chronic diseases
(c) Infectious diseases
(d) Non-infectious diseases
Answer:
(a) Acute diseases: Common cold, eye flu
(b) Chronic diseases: Tuberculosis (TB), asthma
(c) Infectious diseases: Chicken pox, small pox
(d) Non-infectious diseases: Goitre, Cancer

Question 12.
Name two diseases caused by Protozoans. What are their causal organisms.
Answer:
Malaria is caused by Plasmodium and Kala-azar caused by Leishmania Symptoms of malaria are: high fever and shaking chills that can range from moderate to severe, profuse sweating, headache, nausea, vomiting, etc. Symptoms of Kala-azar are breathing difficulty, recurrent fever and skin sores.

Question 13.
Which bacterium causes peptic ulcers? Who discovered the above pathogen for the first time?
Answer:
Heliobacterium pylori cause peptic ulcers. This pathogen was discovered for the first time by Marshall and Warren.

Question 14.
What is an antibiotic? Give two examples.
Answer:
The chemicals secreted by some microorganisms which can kill the bacteria and other disease causing pathogens are called antibiotic. Example: Penicillin, Streptomycin

Question 15.
Fill in the blanks
(a) Pneumonia is an example of ________ disease.
(b) Many skin diseases are caused by ________
(c) Antibiotics commonly block biochemical pathways important for the growth of ________
(d) Living organisms carrying the infecting agents from one person to another are called ________
Answer:
(a) Communicable
(b) Fungi
(c) Bacteria
(d) Vector

Question 16.
Name the target organs for the following diseases
(a) Hepatitis targets ________
(b) Fits or unconsciousness targets ________
(c) Pneumonia targets ________
(d) Fungal disease targets ________
Answer:
(a) Liver
(b) Brain
(c) Lungs
(d) Skin

Question 17.
Who discovered Vaccine’ for the first time? Name two diseases which can be prevented by using vaccines.
Answer:
Edward Jenner discovered vaccine for the first time. Polio, small pox, typhoid, etc. can be prevented by vaccines.

Question 18.
Fill in the blanks:
(a) ________ disease continues for many days and causes effect the on body.
(b) ________ disease continues for a few days and causes short term effect on the body.
(c) ________ is defined as physical, mental and social well-being and comfort.
(d) Common cold is an ________ disease.
(e) Many skin diseases are caused by ________
Answer:
(a) Chronic, long-term
(b) Acute
(c) Health
(d) Infectious
(e) Fungi

Question 19.
Classify the following diseases as infectious or non-infectious.
(a) AIDS
(b) Tuberculosis
(c) Cholera
(d) High blood pressure
(e) Heart disease
(f) Pneumonia
(g) Cancer
Answer:
(a) infectious
(b) infectious
(c) infectious
(d) non-infectious
(e) non-infectious
(f) infectious
(g) non-infectious

Question 20.
Name any two groups of microorganisms from which antibiotics can be extracted.
Answer:
Bacteria and fungi are the microorganisms from which antibiotics can be extracted.

Question 21.
Name any three diseases transmitted through vectors.
Answer:
Filariasis, Dengue, Chikungunya, Malaria, Kala-azar

Why Do we Fall Ill Class 9 Extra Questions Long Answer Type

Question 1.
(a) Give definition of health.
(b) State and explain in brief the four major factors which cause disease.
Answer:
(a) ‘Health’ is defined as a state of physical, emotional, mental and social well being of a person.
(b) The four factors whose non availability or absence can cause disease are:
(i) Proper nourishing food: If the person does not get proper nourishing food and a balanced diet, then disease may affect the person.

(ii) Proper hygienic conditions and cleanliness: If the surroundings are not hygienic and the public cleanliness is ignored in a society, then the individuals living there become more prone to diseases.

(iii) Good social conditions: The society in which the person lives should cater towards a healthy mind set of the members of the society. A bad social environment makes the individuals of the society develop an unhealthy attitude.

(iv) Good economic conditions: Poverty is a major cause of diseases and poor economic conditions increase the chances of spread of diseases in the society due to inadequate food and unhygienic conditions.

Question 2.
(a) Doctors diagnosed that Radha was suffering from HIV-AIDS. List any two methods by which she might have come in contact with the disease. Name the organ affected by this disease.
(b) Why antibiotics cannot be used for its treatment? Justify your answer.
Answer:
(a) AIDS can spread by four ways: Sexual contact, Transfusion of AIDS infected blood, use of infected syringe and from an infected mother to her baby during pregnancy or through breast feeding.

(b) Antibiotics block the biochemical pathways of the microorganism in order to inhibit their growth and kill them. But, the viruses do not employ such biochemical pathways of their own. They utilise the host machinery to multiply themselves. So, antibiotics cannot be used for the treatment of the viral diseases like AIDS.

Question 3.
(a) If a person is suffering from jaundice, name the mode of its transmission and the organ affected by the disease.
(b) List one general mode of prevention of jaundice.
(c) It has been observed that despite the availability of the vaccine of Hepatitis A in the market, it may not be necessary to be given to children by the time they are 5 years old. Why?
Answer:
(a) Mode of transmission of Jaundice: Contaminated water Organ affected by Jaundice: Liver

(b) Access to pure drinking water can prevent jaundice.

(c) Most of the children of India are already exposed to the hepatitis A virus through the drinking water and their immune system helps to develop immunity against the disease by the time they are five years old. So, it is not necessary to give them the hepatitis A vaccine.

Question 4.
Give an account of malaria, giving its causative agent, symptoms and control measures.
Answer:
Malaria is a protozoan disease caused by Plasmodium species. It gets transmitted by a vector called as the female Anopheles mosquito. The symptoms of malaria are high fever and body ache. The patient feels chills and shivering at regular time intervals. The disease can be controlled by eliminating the breeding grounds of mosquitoes, using mosquito nets or mosquito repellents at home, taking a dose of quinine medicine as prescribed by the doctor.

Question 5.
(a) Name two air-borne diseases. How does the disease causing microbes spread through air?
(b) How does HIV virus spread from a patient to a healthy person?
(c) How does the immune system of our body function?
Answer:
(a) Common cold, tuberculosis, pneumonia are some air-borne infections. They spread from one person to another when an infected person releases droplets into air while coughing or sneezing and these droplets get inhaled by a healthy person standing close by. The microbes start a new infection in the healthy person.

(b) HIV can spread by the following ways: Sexual contact, transfusion of AIDS infected blood, from an infected mother to her baby during pregnancy or through breast feeding, use of infected syringe.

(c) The immune system gets activated on encountering a disease causing microbe or on infection and recruits many cells to the affected tissue by a process called as inflammation. This results in pain, swelling, fever, etc., but ultimately it results in killing the disease causing microbe and prevent spread of infection.

Question 6.
(a) Discuss briefly the principle of immunisation.
(b) Mention any two diseases that can be prevented by immunisation.
Answer:
(a) The process by which immunity or resistance to a disease is developed in an individual by administration of biological preparations called vaccines is known as immunisation. In this process, a harmless or dead pathogen is introduced in the body of the organism by vaccination. The immune system of the organism gets activated and produces antibodies against the pathogen to kill it.

These antibodies remain in the memory of the immune system of the individual and in the case of any subsequent infection by the same microbe, these antibodies act quickly and more vigorously to kill the microbe. In this way, the microbe is not able to infect the person and the person gets immunised against the disease.

(b) Two diseases prevented by immunisation are: Measles and polio. Some other diseases which can be prevented by vaccination are diphtheria, pertusis, whooping cough, hepatitis, tetanus, etc.

Question 7.
Explain giving reasons
(а) Balanced diet is necessary for maintaining healthy body.
(b) Health of an organism depends upon the surrounding environmental conditions.
(c) Our surrounding area should be free of stagnant water.
(d) Social harmony and good economic conditions are necessary for good health.
Answer:
(a) Balanced diet provides raw materials and energy in appropriate amount needed for the proper growth and development of the body. It contains the nutrients like the protein, carbohydrates, fats, minerals etc., in the right amount which helps in the proper growth and functions. This ensures a good health of the individual.

(b) The physical, mental and the social well being of a person is affected by the surrounding environmental conditions. Since, these factors determine the health of a person, we can say that the health of a person depends on the environmental conditions. For example, Unhygienic surroundings as breeding grounds for disease causing organisms and their vectors can harm our health.

(c) Stagnant water is a source of many water-borne diseases and acts as breeding place for many insect vectors which can cause diseases in human beings. So, our surrounding area should be free of stagnant water.

(d) Social harmony ensures that the mental tensions and problems do not surround a person and friendly relations are maintained among the individuals of the society. They strive for the growth and well being of each other and thus better health is maintained in such environment and surroundings. Better economic conditions enable a person to invest more to attain good health by eating nutritive food, ensure protection from diseases, get better medical facilities, etc. So, health of a person is better maintained if economic conditions are good.

Question 8.
What is a disease? How many types of diseases have you studied? Give examples.
Answer:
Any condition that disturbs the normal functioning of the organism or its organs is called a disease. Diseases can be classified as acute, chronic, infectious, non-infectious, etc. The diseases which are for short duration are called acute whereas the diseases which persist for a long time are called chronic diseases, example common cold (acute) and tuberculosis (chronic).

The diseases which can be transmitted from one person to another are called infectious diseases whereas the ones which cannot be transmitted are called non-infectious diseases, example cancer and goitre respectively.

Question 9.
What do you mean by disease symptoms? Explain giving two examples.
Answer:
The physical disturbances or the visual changes which indicate the existence of a disease are called the symptoms of the disease.
Example:

• High fever and chills is a symptom of malaria.
• Appearance of lesions on the skin is a symptom of chickenpox.

Question 10.
Why is the immune system essential for our health?
Answer:
Immune system is essential as it helps our body to fight against disease causing microbes. It protects our body by secreting chemicals called antibodies or other substances which protect us from harmful microbes.

Question 11.
What precautions will you take to justify “prevention is better than cure”?
Answer:
The precautions which can be taken to protect ourselves from the disease are:

• Maintaining personal hygiene as well as clean surroundings.
• Being aware about diseases, their symptqms and the organism which causes then.
• Eating a balanced diet.
• Timely vaccination and regular medical, check-up.

Question 12.
Why do some children fall ill more frequently than others living in the same locality?
Answer:
The reasons due to which some children fall ill more frequently than others living in the same locality can be:

• Poor and inefficient immune system.
• Unhealthy food habits and not taking balanced diet.
• Not maintaining personal hygiene.

Question 13.
Why are antibiotics not effective for viral disease?
Answer:
The mode of action of the antibiotics is blocking the biosynthetic pathways of the bacteria and other microbes. However, viruses do not have such biochemical pathways or have very few biochemical mechanisms of their own, hence viruses are unaffected by antibiotics.

Question 14.
Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. Explain.
Answer:
Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease because the immune system becomes active when it encounters a pathogen. If the immune system of the organism is able to ward off the disease causing microbe, then the disease will not occur and the person will remain disease-free. So, a strong immune system can ensure that we do not suffer from diseases even if we are exposed to infectious microbes.

Question 15.
Give any four factors necessary for a person to be healthy.
Answer:
The four factors necessary for a person to be healthy are:

• Proper nourishment and a balanced diet which help to provide a strong immune system.
• Maintaining personal hygiene to protect ourselves from infectious microbes.
• Timely vaccination against various diseases.
• Maintaining community hygiene and clean surroundings will to prevent the incidence of waterborne and the air-borne diseases.

Question 16.
Why is AIDS considered to be a ‘Syndrome’ and not a disease?
Answer:
The causative organism of AIDS is a virus called the HIV which gets transmitted through sexual contact, transfusion of contaminated blood, intravenous syringes used by drug addicts and from a mother suffering with AIDS to her child, spread to lymph nodes all over the body. The virus attacks the immune system of the organism and makes it so weak that it cannot fight against even the minor infections. Due to this even a small cold can develop into pneumonia or minor stomach infection may lead to severe diarrhoea and blood loss in stools.

Ultimately the immune system becomes very weak and leads to the death of the person suffering from AIDS. Many diseases simultaneously develop in such a person, so there is no specific disease symptom but a number of symptoms occur in the person. This group of symptoms are called as ‘syndrome’. So, AIDS is not a disease, it is a syndrome.

Why Do we Fall Ill Class 9 Extra Questions HOTS

Question 1.
The symptoms seen in a patient are high fever, constipation and stomach pain. A doctor wants to confirm whether the patient is suffering from Amoebiasis or typhoid. How can the doctor confirm it?
Answer:
The doctor can advise the patient to get a widal test done which helps to confirm the presence of typhoid causing microorganism in the body. If typhoid is ruled out then the patient is most likely to suffer from Amoebiasis.

Question 2.
Name the disease:
(a) that spreads by sexual contact but not by casual contact like handshake.
(b) that can be caused by virus, bacteria or protozoa.
(c) that can be caused due to bite of stray dog.
Answer:
(a) AIDS
(b) Diarrhoea
(c) Rabies

Question 3.
A mother who had suffered from chicken pox in her childhood, is now taking care of her child, who is suffering from the same disease. What are the chances of her mother having chicken pox? Explain.
Answer:
The mother will not suffer from chicken pox as she has become immune to chicken pox. During the first infection, her immune system develops antibodies against chicken pox. These antibodies respond with more vigour during the next infection, eliminate the microbe and thus prevent the person from the disease.

Question 4.
Name the disease:
(a) in which the liver of the person is the target.
(b) in which saliva of the infected animal spreads infection.
(c) against which BCG vaccine is given.
(d) for which widal test is done.
(e) in which sexual contact spreads the disease but not the physical contact in form of handshakes or hugging.
Answer:
(a) Jaundice and hepatitis
(b) Rabies
(c) Tuberculosis
(d) Typhoid
(e) AIDS

Question 5.
The immune system of a patient has been damaged by a virus. What is the probable disease which would have led to this effect on the immune system? What are the ways by which the pathogen would have been transferred into the individual?
Answer:
The disease is most likely to be AIDS caused by the HIV virus which damages the immune system of the person.

AIDS can be spread in four ways: Sexual contact, transfusion of AIDS infected blood, from an infected i mother to her baby during pregnancy or through breast feeding.

Question 6.
A patient bitten by a stray animal complained of excessive salivation, restlessness and a fear of water. What can be the probable disease and its cause? How can such disease be treated or controlled?
Answer:
The patient is probably suffering from rabies caused by the rabies virus. The disease can be controlled by ensuring proper vaccination of stray animals like dogs. The disease can be treated by timely administration of anti rabies vaccine.

Question 7.
A patient went to a doctor and complained of having a persistent cough, blood in sputum, breathlessness and loss of body weight. Name the disease and the causative microbe. How is the disease transmitted? Which vaccine is given to develop resistance against the disease?
Answer:
The disease from which the patient is suffering is Tuberculosis (T.B.) and the causative microbe is . a bacteria called Mycobacterium tuberculosis.. The disease gets transmitted when a healthy person inhales the droplets released by an infected person on coughing, sneezing or while talking. The vaccine i called BCG is given to develop resistance against the disease.

Question 8.
A child was suffering from loose motions, frequent vomiting, feeling of nausea and watery diarrhoea which led to an excessive loss of fluids from his body. Name the disease and its causative microbe. What measures, can be taken to treat this disease? How can one avoid getting infected by the disease?
Answer:
The person is infected with disease called cholera which is caused by a virus called Vibrio cholerae. The measures which can be taken for treatment of the disease are: Giving ORS-Oral rehydration solution to the patient and giving antibiotics prescribed by the doctor. The disease can be avoided by eating clean and hygienic food and timely immunisation against the disease.

Why Do we Fall Ill Class 9 Extra Questions Value Based (VBQs)

Question 1.
An HIV infected employee was dismissed from service by the employer. The colleagues of the employee in the office intervened and convinced the boss of the company to reinstate the services of the employee as HIV is not transmitted by mere physical contact. They told the employer that such person should not be made a victim of social stigma on contracting the disease.
(i) Name the disease which the employee was suffering from.
(ii) How does the disease get transmitted from one person to another?
(iii) What values are shown by the colleagues of the employee?
Answer:
(i) AIDS: Acquired immunodeficiency syndrome.

(ii) The disease gets transmitted by four ways:
(a) Sex with multiple partners.
(b) Transfusion of HIV contaminated blood.
(c) Use of HIV contaminated syringe.
(d) From infected mother to her child at the time of delivery of the baby.

(iii) The values shown by the colleague of the employee are: awareness, helpfulness, empathy and knowledge about their rights.

Question 2.
Rohit and’ Mayank are roommates in the hostel. Mayank is an avid reader of science magazines and articles. Mayank immediately took Rohit to a doctor when Rohit complained of tiredness, nausea, vomiting and pale eyes. What is the probable disease Rohit was suffering from? Name the causative microbe. What values are shown by Mayank?
Answer:
The symptoms of Rohit show that he was suffering from Jaundice. The microbe which causes the disease is virus. The values shown by Mayank are awareness, scientific temper, concern for others and helpful nature.

Question 3.
The parents of a new bom child were afraid to take their child for vaccination as someone told them that the vaccine contains harmful germs. However, when they consulted Dr. Shweta, she listened to them patiently and then cleared their doubts about vaccines. She told them that the vaccines only contain dead germs or inactivated germs which do not cause the disease. How do the dead germs in vaccines protect from diseases? What are the values shown by Dr. Shweta?
Answer:
The dead or the inactivated germs in the vaccines stimulate our immune system to develop antibodies against the disease causing microbes present in the vaccine and store the antibodies for action during any subsequent infection. In this way the vaccines provide immunity to the person against the disease. The values shown by Dr. Shweta are concern for others, helpfulness and patience.

Question 4.
Megha’s told her that he had been feeling tired, breathless, had persistent cough and blood was coming out in his sputum. She told him that these are symptoms of an infectious disease and advised him to consult a doctor. She also took him for diagnostic tests prescribed by the doctor. The helps was diagnosed as suffering from an infectious disease. He took the medicines prescribed by the doctor and got cured of the disease.
(i) Name the most likely disease and microbe from which the help suffered?
(ii) How does the disease get transmitted?
(iii) What are the values depicted by Megha?
Answer:
(i) The disease is most likely Tuberculosis caused by bacteria.

(ii) The disease gets transmitted when a healthy person inhales the droplets released into air by an infected person while coughing or sneezing.

(iii) Megha shows a helpful nature, scientific attitude, concern for others and sympathetic nature.

Question 5.
The municipality of an area advised the residents of the area to eliminate the breeding grounds of mosquitoes and use mosquito repellents in homes to avoid a disease which results in chills and recurring fever in patients. The children of the area formed teams which inspected the surrounding areas and put few drops of oil or petrol on stagnant water pools of the area.
(i) Name the disease, causative organism and the vector of the disease which was spreading in the area.
(ii) How do the drops of petrol or oil on stagnant water prevent the spread of the disease?
(iii) What are the values shown by the students?
Answer:
(i) The disease is Malaria caused by Plasmodium and transmitted by the vector female Anopheles mosquito.

(ii) The drops of oil or petrol in the stagnant water pools kill the larvae of the mosquito as they will not be able to breathe.

(iii) The values shown by the children are: public good, helpful attitude, scientific temper and work for social good.

In this page, we are providing Sound Class 9 Extra Questions and Answers Science Chapter 12 pdf download. NCERT Extra Questions for Class 9 Science Chapter 12 Sound with Answers will help to score more marks in your CBSE Board Exams.

Class 9 Science Chapter 12 Extra Questions and Answers Sound

Extra Questions for Class 9 Science Chapter 12 Sound with Answers Solutions

Sound Class 9 Extra Questions Very Short Answer Type

Question 1.
What are longitudinal waves?
Answer:
A wave in which the particles of the medium vibrate back and forth in the ‘same direction’ in which the wave is moving, is called as a longitudinal wave.

Question 2.
What are transverse waves?
Answer:
A wave in which the particles of the medium, vibrate up and down ‘at right angle’ to the direction in which the wave is moving, is called a transverse wave.

Question 3.
Define wavelength. What is its symbol and its SI unit?
Answer:
The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength. The wavelength is denoted by (Greek letter ‘lambda’). Its SI unit is the metre (m).

Question 4.
Define frequency. What is its symbol and its SI unit?
Answer:
The number of complete waves (or cycles) produced per second is called a frequency of sound waves. It is denoted by f. The SI unit of frequency is hertz (Hz).

Question 5.
What is one hertz?
Answer:
A vibrating body producing 1 wave per second is said to have a frequency of 1 Hz.

Question 6.
Define amplitude. What is its symbol and its SI unit?
Answer:
The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of wave. It is denoted by A. The SI unit is the metre (m).

Question 7.
What is ‘audible’ sound?
Answer:
The sound which we are able to hear is called ‘audible’ sound. The audible range of sound for human beings extends from about 20 Hz to 20000 Hz.

Question 8.
What do you mean by an echo?
Answer:
The repetition of sound caused by the reflection of sound waves is called an ‘echo’.

Question 9.
What do you understand by the terms “compression” and rarefaction?
Answer:
A region of high pressure of a medium when a sound wave travels through it is called compression.
A region of low pressure of a medium when a sound wave travels through it is called rarefaction.

Question 10.
What do you understand by the pitch of a sound?
Answer:
Pitch of a sound is the characteristic of sound that depends on the frequency received by a human ear.

Question 11.
What do you understand by the loudness of sound?
Answer:
The amplitude of the vibrating body determines the loudness of the sound. Larger the amplitude of vibration, larger the loudness of the sound produced.

Question 12.
Define the characteristic “timbre” or “quality” of a sound.
Answer:
Quality or timbre is a characteristic of a sound which enables us to distinguish between two sounds of the same loudness and pitch.

Question 13.
What is Sonar?
Answer:
Sonar is a device that uses ultrasonic wave to measure the distance, direction and speed of the underwater object.

Question 14.
What is Echocardiography?
Answer:
The technique of obtaining images of the heart by using the reflection of ultrasonic waves from various parts of the heart is called echocardiography.

Question 15.
What is ultrasonography?
Answer:
The technique of obtaining images of internal organs of the body by using echoes of ultrasonic waves is called ultrasonography.

Question 16.
What is a stethoscope?
Answer:
The stethoscope is a medical instrument used for listening sounds produced within the body, chiefly in the heart or lungs.

Question 17.
What are infrasonic waves?
Answer:
The waves of frequency less than 20 Hz are called infrasonic waves.

Question 18.
What is ultrasound?
Answer:
The waves of frequency greater than 20,000 Hz are called ultrasonic waves or ultrasound.

Question 19.
Speed of sound is more on a hotter day. Explain why.
Answer:
Speed of sound increases with increase in temperature.

Question 20.
WrIte down the SI unit of (i) frequency (ii) wavelength.
Answer:
SI unit of wavelength is m and frequency is Hz.

Sound Class 9 Extra Questions Numericals

Question 1.
The sound produced by a thunderstorm is heard 10 s after the lightning is seen. Calculate the approximate distance of the thunder cloud. (Given the speed of sound = 340 ms’).
Ans. Given, t = 10 s
υ = 340 m/s
distance, x = υ x t = 340 x 10 = 3400 m.

Question 2.
What is the frequency of wave with time period 0.025 s?
Answer:
Given, t = 0.025 s
frequency, v = \(\frac{1}{t}=\frac{1}{0.025}\) = 40 Hz.

Sound Class 9 Extra Questions Short Answer Type 1

Question 1.
What is sound? When is the sound produced? Give examples.
Answer:
The sensation felt by our ears is called sound. A sound is a form of energy which makes us hear. When an object is set into vibrations, the sound is produced. For example, the vibrating diaphragm of a drum produces sound, the vibrating string of a guitar produces sound, the vibrating diaphragm of speakers of a radio produce sound, the vibrating end of a drilling machine produces sound, etc.

Question 2.
State the conditions to hear an echo.
Answer:
The conditions to hear an echo are:

1. Echo can be heard only if it is produced at least \(\frac {1}{10}\) th of a second (0.1 s) after the original sound.

2. The speed of sound in air is 344 m/s. Let us calculate the minimum distance from the reflecting surface, which is necessary to hear an echo.

∴ Distance travelled = 344 x \(\frac {1}{10}\) = 34.4 metres
Thus, the distance travelled by the sound in \(\frac {1}{10}\) th of a second is 34.4 m. This means that the minimum distance between the source of the sound and the listeners should be 17.2 metres.

3. Echo can be heard only if the reflecting surface is large.

Question 3.
Bats search out prey and fly in the dark night by emitting ultrasound. Explain.
Answer:
Bats search out prey and fly in the dark night by emitting and detecting reflections of ultrasonic waves. The high-pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat’s ear. The nature of reflections tells the bat where the obstacle or prey is and what it is like.

Question 4.
Mention one advantage and one disadvantage of reverberation.
Answer:
A certain amount of reverberation improves the quality of sound of orchestral and choral music. However excessive reverberation makes the speech or music indistinct.

Question 5.
How does a megaphone works?
Answer:
A megaphone works on the principle of reflection of sound. In this instrument, a tube followed by a conical opening reflects sound successively to guide most of the sound from the source in the forward direction towards the audience.

Sound Class 9 Extra Questions Numericals

Question 1.
If the velocity of sound in air is 340 ms^-1. Calculate
1. wavelength when the frequency is 256 Hz.
2. frequency when the wavelength is 0.85 m.
Answer:
Given,
velocity of sound, υ = 340 m/s
1. v = 256 Hz
using, υ = λ v
λ = \(\frac {υ}{λ}\) = \(\frac {340}{256}\) = 1.33m

2. λ = 0.85
using, u = λv
λ = \(\frac {υ}{λ}\) = \(\frac {340}{0.85}\) = 400Hz

Question 2.
30 waves pass through a point in 3 seconds. If the distance between two crests is 2 m. Calculate
(a) frequency
(b) wavelength.
Answer:
30 waves in 3 seconds
υ = \(\frac {30}{3}\) = 10Hz
∴ λ = 2m.

Sound Class 9 Extra Questions Short Answer Type 2

Question 1.
What is the reflection of sound? State the laws of reflection.
Answer:
The bouncing back of sound from a hard surface is called a reflection of sound. The laws of reflection are:
1. The incident sound wave, the reflected sound wave and the normal at the point of incidence, all lie in the same plane.
2. The angle of incidence of sound is always equal to the angle of reflection of sound.

Question 2.
On what factor does the speed of sound depend?
Answer:
The speed of sound depends upon the following:

• The nature of the material (or medium) through which it travels. In general, sound travels fastest in solids, slower in liquids and slowest in gases.
• The humidity of the air. As the humidity of air increases, sound travels faster. Sound has more speed in humid air than in dry air.
• The temperature. The speed of sound in air at 0°C is 332 m/s whereas at 20°C, it is 344 m/s. Thus, as the temperature rises, the speed of sound also increases.

Question 3.
Write a note on ‘ultrasonic sounds’.
Answer:

• The sounds of frequencies higher than 20,000 Hz are known as ‘ultrasonic sounds’ (or just‘ultrasounds’).
• Human beings cannot hear ultrasonic sounds. Children under the age of five and some animals, such as dogs can hear sounds up to 25,000 Hz.
• As people grow older, their hearing sensation for higher frequencies becomes weaker.
• Ultrasonic sounds are used by dolphins, bats and porpoises to navigate in dark and to catch their prey.
• Some moths can hear high-frequency ultrasonic squeaks of the bat and know when a bat is flying nearby and are able to escape capture. Rats also play games by producing ultrasound.

Question 4.
Write three differences between transverse and longitudinal waves.
Answer:
Transverse waves:

• In the transverse waves, the particles of the medium vibrate perpendicular to the direction of wave motion.
• These waves travel in the form of alternate crest and trough.
• These waves can be transmitted through solid or liquid surfaces.

Longitudinal waves:

• In longitudinal waves, the particles of the medium vibrate along the direction of wave motion.
• These waves travel in the form of alternate compression and rarefactions.
• These waves can be transmitted through all the three types of media viz., solid, liquid and gases.

Question 5.
Write down three differences between a sound wave and lightwave.
Answer:
Sound wave:

• It travels in the form of longitudinal waves.
• It requires a medium for its propagation.
• It travels through air with a speed of 332 propagation. m/s at 0°C.

Lightwave:

• It travels in the form of a transverse wave.
• It does not require a medium for its propagation.
•  It travels through air with a speed of nearly 3 x 10⁸ m/s.

Sound Class 9 Extra Questions Long Answer Type

Question 1.
State three applications of reflection of sound.
Answer:
1. Megaphone and a bulb horn: Megaphones or loudhailers, horns, musical instruments such as trumpets and she Hana is, are all designed to send sound in a particular direction without spreading it in all directions, as shown in the figure. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.

2. Stethoscope: Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs. In stethoscopes, the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflections of sound, as shown in the figure.

3. Soundboard: Generally the ceiling of concert halls, conference halls and cinema halls are curved so that sound after reflection reaches all corners of the hall, as shown in the figure. Sometimes a curved soundboard may be placed behind the stage so that the sound, after reflecting from the soundboard, spreads evenly across the width of the hail (Fig).

Question 2.
State the applications of ultrasound.
Answer:
Ultrasounds are high-frequency waves. Ultrasounds are able to travel along well-defined paths even in the presence of obstacles. Ultrasounds are used extensively in industries and for medical purposes.

1. Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd-shaped parts, electronic components, etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to high frequency, the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned.

2. Ultrasounds can be used to detect cracks and flaws in metal blocks. Metallic components are generally used in the construction of big structures like buildings, bridges, machines and also scientific equipment. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure.

Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.

3. Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.

4. An ultrasound scanner is an instrument which uses ultrasonic waves from getting images of internal organs of the human body. A doctor may image the patient’s organs such as liver, gall bladder, uterus, kidney, etc. It helps the doctor to detect abnormalities, such as stones in the gall bladder and kidney or tumours in different organs.

In this technique, the ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density. These waves are then converted into electrical signals that are used to generate images of the
organ.

These images are then displayed on a monitor or printed on a film. This technique is called ‘ultrasonography’. Ulträsonography is also used for examination of the foetus during pregnancy to detect congenital defects and growth abnormalities.

5. Ultrasound may be employed to break small ‘stones’ formed in the kidneys into fine grains. These grains later get flushed out with urine.

Sound Class 9 Extra Questions HOTS

Question 1.
Why do we hear the sound produced by the humming bees while the sound of vibrations of a pendulum is not heard?
Answer:
This is because the frequency of the sound produced by humming bees lies in audible range and frequency of the sound of vibrations of pendulum lies in the infrasonic region.

Question 2.
Sounds of same loudness and pitch but produced by different musical instruments like a violin and flute are distinguishable.
Answer:
It is the quality of sound which enables us to distinguish between two sounds of the same loudness and pitch.

Question 3.
Which of the two graphs (a) and (b) shown in the figure below represents the human voice is likely to be the male voice? Give a reason for your answer. (NCERT Exemplar)

Answer:
Graph a represents the male voice because the frequency of male voice is less than that of the female voice.

Question 4.
The given graph (Fig.) shows the displacement versus time relation for a disturbance travelling with velocity 1500 ms^-1. Calculate the wavelength of the disturbance. (NCERT Exemplar)

Answer:
Here, frequency, u = \(\frac {1}{T}\)
T = 2 ms = 2 x 10^-6 s
Hence υ = \(\frac{1}{2 \times 10^{-6}}\) = 5 x 10⁵ Hz
using relation, λ. = \(\frac{v}{v}=\frac{1500}{5 \times 10^{5}}\) = 3 x 10^-2 m

Question 5.
For hearing the loudest ticking sound heard by the ear, find the angle x in the Figure. (NCERT Exemplar)

Answer:
Here angle of incidence,
i = 90° – 50° = 40°
Angle of incidence (i) or Angle of reflection (x)
x = i = 40°.

Sound Class 9 Extra Questions Value Based (VBQs)

Question 1.
Sumeet went to a hill station with his parents and elder sister Kirti. He was experiencing the scenic beauty of a hill station for the first time. One day they were walking in a forest area, Sumeet loudly called out ‘Kirti Didi’. He was surprised that he could distinctly hear the same sound twice. He discussed this with his sister and she explained the reason behind this echo.
Answer:
(a) The repetition of sound caused by the reflection of sound waves is called an echo.
(b) Kirti is intelligent and helpful.

Question 2.
Tinku studies in class 9th. Once he was suffering from cold and cough and was running a high temperature. His mother took him to a doctor. The doctor examined the chest and back of Tinku with the help of a device ‘stethoscope’. While examining with stethoscope doctor asked Tinku to take longer breaths. After examining Tinku, the doctor prescribed some drugs.

By regular use of these drugs, Tinku was normal within four days. But he could not understand the purpose of being examined by the use of a stethoscope. During winter break his cousin Honey, who was studying in a medical college, visited their place. On the request of Tinku, Honey explained the purpose of the stethoscope and its action.
(a) What is a stethoscope?
(b) What quality was shown by Honey?
Answer:
(a) The stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs.
(b) Honey is intelligent and helpful.

Question 3.
On a hot summer afternoon, a man was shouting through a megaphone. He was ‘zip-repairer’. As Arshi was preparing for her examination, she got disturbed. She inquired her father about the instrument being used by the ‘zip-repairer’. The father told her that it was a megaphone also known as ‘loud hailer’.
(a) State the principle on which the megaphone works.
(b) Why did Arshi get disturbed?
Answer:
(a) Megaphone works on the principle of multiple reflections.
(b) Arshi got disturbed by noise pollution.

Question 4.
Reena’s grandmother took her mother to a doctor as she was four months pregnant for ultrasonography. But she showed her interest in determining whether the child is a boy or a girl. The doctor was annoyed and refused to disclose the gender of the child.
(a) What is ultrasonography?
(b) Write down the values shown by the doctor.
Answer:
(a) The technique of obtaining images of internal organs of the body by using echoes of ultrasound waves is called ultrasonography.
(b) A Doctor is a law-abiding person.

In this page, we are providing Work, Power And Energy Class 9 Extra Questions and Answers Science Chapter 11 pdf download. NCERT Extra Questions for Class 9 Science Chapter 11 Work, Power And Energy with Answers will help to score more marks in your CBSE Board Exams.

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

Extra Questions for Class 9 Science Chapter 11 Work, Power And Energy with Answers Solutions

Work, Power And Energy Class 9 Extra Questions Very Short Answer Type

Question 1.
Define the following terms.
(a) Work was done
(b) Energy
(c) Mechanical energy
(d) Kinetic energy
(e) Potential energy
(f) Power
(g) Commercial unit of energy.
Answer:
(a) Work done: Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.
(b) Energy: Energy of a body is defined as the capacity or ability of the body to do work.
(c) Mechanical energy: Mechanical energy includes kinetic energy and potential energy.
(d) Kinetic energy: The energy possessed by a body by virtue of its motion.
(e) Potential energy: The energy possessed by a body due to its position or configuration.
(f) Power: Power is defined as the rate of doing work or the rate of transfer of energy.
(g) Commercial unit of energy: The energy used in households, industries, and commercial establishment are usually expressed in kilowatt-hour.
1 kWh 1 unit = 3.6 x 10⁶J

Question 2.
Write down the type of energy stored in
(a) spring of a watch
(b) flowing water
(c) rolling stone
(d) raised hammer
(e) running athlete
Answer:
(a) potential energy
(b) kinetic energy
(c) kinetic energy
(d) potential energy
(e) kinetic energy.

Question 3.
What will be the kinetic energy of a body when its mass is made four-time and the velocity is doubled?
Answer:
Initial kinetic energy,
\(E_{K_{i}}=\frac{1}{2} m v^{2}\)
Final kinetic energy,
\(E_{K_{f}}=\frac{1}{2}(4 m) \times(2 v)^{2}\)
= 16 x \(\frac {1}{2}\)mυ²
\(E_{K_{f}}=16 E_{K_{i}}\)

Question 4.
If we lift a body of 7 kg vertically upwards to a height of 10 m, calculate the work done in lifting the body.
Answer:
Given, m = 7 kg
s = 10m
Workdone, W = F x s
E = mg x s
W = 7 x 10 x 10 J
w = 7000 J

Question 5.
State the transformation of energy that takes place when

• Green plants prepare their food.
• Head of a nail hammered hard and it becomes hot.

Answer:

• Solar energy of sun into chemical energy.
• The kinetic energy of the hammer into heat energy.

Question 6.
How much work is done by a man who tries to push the wall of a house but fails to do so?
Answer:
W = Fs = 0
As there is no displacement.

Question 7.
Establish a relationship between SI unit and commercial unit of energy.
Answer:
SI unit of energy is joule and the commercial unit of energy is the joule.
1kWh = 1000 W x 3600 s = 3.6 x 10⁶J

Question 8.
Write down the energy transformation taking place
(a) In electric bulb
(b) In torch
(c) In the thermal power station
(d) In solar cell
(e) Electric heater
Answer:
(a) Electricity into light energy
(b) The chemical energy of the cell into light and heat energy
(c) The chemical energy of fuel into electricity
(d) Solar energy into electricity
(e) Electricity into heat energy.

Question 9.
A body of mass m is moving in a circular path of radius r. How much work is done on the body?
Answer:
Zero. This is because the centripetal force acting on the body is perpendicular to the displacement of the body.

Question 10.
A horse of mass 200 kg and a dog of mass 20 kg are running at the same speed. Which of the two possesses more kinetic energy? How?
Answer:
The kinetic energy of the horse is more as kinetic energy is directly proportional to mass.

Question 11.
What is the condition for work done to be positive?
Answer:
For positive work, the angle between force and displacement should be acute.

Question 12.
Write down the relation between kinetic energy and momentum of a body.
Answer:
\(E_{K}=\frac{p^{2}}{2 m}\)
E_k = kinetic energy of a body
p = momentum of the body
m = mass of the body.

Question 13.
A cyclist comes to a skidding stop at 50 m. During this process, the force on the cycle due to the road is 1000 N and is directed opposite to the motion. How much work does the road do on the cycle?
Answer:
Given,
Displacement, s = 50 m
Force, F = – 1000 N
Workdone, W = F x s
W = -1000 x 50J
W = 50000J

Question 14.
A boy pushes a book by applying a force of 40 N. Find the work done by this force as the book is displaced through 25 cm along the path.
Answer:
Given, Force (F) = 40 N
Displacement (s) = 25 cm = x 10^-2 m
Workdone, W = F x s
= 40 x 25 x 10^-2
= 10J
∴ W = 10J

Work, Power And Energy Class 9 Extra Questions Short Answer Type 1

Question 1.
State law of conservation of energy and law of conservation of mechanical energy.
Answer:
Law of conservation of energy: Energy can neither be created nor be destroyed, it can only be transformed from one form to another.
Conservation of mechanical energy: If there is no energy, then the mechanical energy of a system is always constant.

Question 2.
Define (a) 1 joule (b) 1 watt.
Answer:
(a) 1 joule is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.
(b) 1 watt is the power of an agent, which does work at the rate of 1 joule per second.

Question 3.
Write down SI unit of the following quantities.
(a) work
(b) kinetic energy
(c) potential energy
(d) power
Answer:
(a) joule (J)
(b) joule (J)
(c) joule (J)
(d) watt (W).

Question 4.
What is the sequence of energy change that takes place in the production of electricity from adam?
Answer:
The potential energy of stored water is converted into the rotational kinetic energy of turbine blades. The rotational kinetic energy of turbine blades is finally converted into electric energy by the generator.

Question 5.
A light and a heavy object have the same momentum. Find out the ratio of their kinetic energies. Which one has larger kinetic energy?
Answer:
The relation between kinetic energy and momentum
Given,

Question 6.
Why a man does not do work when he moves on a level road while carrying a box on his head?
Answer:
When a man carries a load on his head, the angle between displacement (s) and force (F) is 900. Therefore work done is zero.

Work, Power And Energy Class 9 Extra Questions Numericals

Question 7.
If an electric iron of 1200 W is used for 30 minutes every day, find electric energy consumed in the month of April.
Answer:
Given,
Power, P = 1200 W
time, t = 30 minutes
Power, p = \(\frac {W}{t}\) = \(\frac {E}{t}\)
E = P x t
Energy consumed, E = 1200 x 30 x 60
= 2.16 x 10⁶J = 2.16MJ

Question 8.
What is work done by a force of gravity in the following cases?
(a) Satellite moving around the Earth in a circular orbit of radius 35000 km.
(b) A stone of mass 250 g is thrown up through a height of 2.5 m.
Answer:
(a) Zero
(b) Given,
mass (m) = 250 g = 0.25 kg
height (h) = 2.5 m
Workdone, W = Fs = mgh
= 0.25 x 10 x 2.5
= 6.25 J
W = 625 J

Question 9.
A car and a truck have kinetic energies of 8 x 10 J and 9 x 10 J respectively. If they are brought to a halt at the same distance, find the ratio of the force applied to both the vehicles.
Answer:
Given,
Kinetic energy of car, \(\frac {1}{2}\) = 8 x 10 J
Kinetic energy of truck, \(\frac {1}{2}\) = 9 x 10 J
W = Fs
Work done,

Question 10.
A bus of mass 10,000 kg is moving with a velocity 90 km/h. Calculate the work done to stop this bus.
Answer:
Given,
mass of object, m = 1000 kg
Initial velocity of object, u = 90 km/h

= 25 m/s
Work done = \(\frac {1}{2}\) mυ² – \(\frac {1}{2}\) mu² = 0 – \(\frac {1}{2}\) x 10000 x (25)² = 312.5 x 10⁴ J

Work, Power And Energy Class 9 Extra Questions Short Answer Type 2

Question 1.
The velocity of a body moving in a straight line is inereásed by applying constant force F, for some distance in the direction of motion. Prove that the increase ¡n the kinetic energy of the body is equal to the work done by the force on the body.
Answer:
Let us consider an object lying on a frictionless surface having mass ‘m’.

A force of constant magnitude ‘F’ is acting on the body. Here initial velocity of the body is u and the final velocity is u. As there is no dissipative forces, work on the body will be stored in the form of a change in kinetic energy. It can be proved as
W = Fs …………(1)
and hence from the equation of motion
υ² – u² = 2as
s = \(\frac{v^{2}-u^{2}}{2 a}\) ………….(2)
Asweknowthat F = ma
Using (1), (2) and (3),
W = ma x \(\frac{v^{2}-u^{2}}{2 a}\)
= \(\frac {1}{2}\) m (υ² – u²)
= \(\frac {1}{2}\)mυ² – \(\frac {1}{2}\)mu²
= change in kinetic energy

Question 2.
Derive an expression for potential energy. Write Its SI unit.
Answer:
When work is done on the body, the work is stored in the form of energy. Consider an object of mass, m. Let it be raised through a height, h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object, mg. The object gains energy equal to the work done on it. Let the work done on the object against gravity h be W.
i.e., W = force x displacement = mgh

Since work done on the object is equal to mgh, an energy equal to mgh units is gained by the object. This is the potential energy (E_p) of the object.
∴ E_p = mgh
SI unit of potential energy is the joule (J).

Work, Power And Energy Class 9 Extra Questions Numericals

Question 3.
A girl having a mass of 35 kg sits on a trolley of mass 5 kg. The trolley is given an initial velocity of 4 ms1 by applying a force. The trolley comes to rest after traversing a distance of 16 m.
(a) How much work is done on the trolley?
(b) How much work is done by the girl?
Answer:
Given, mass of girl, m = 35 kg
mass of trolley, m = 5 kg.
initial velocity of trolley, u = 4 m/s

(a) using work done = change in kinetic energy
W = \(E_{K_{f}}-E_{K_{i}}\)
= o – \(\frac {1}{2}\) x 40 x (4)² = – 320
∴ W = 320 J_J
(b) Work done by the girl = 0.

Question 4.
Express kilowatt in terms of joule per second. A 150 kg car engine develops 500 W for each kg. What forces does it exert in moving the car at a speed of 20 ms^-1?
Answer:
1 kW = iooo w = 10³ J/S
Given, mass (m) = 150 kg
power (P) = 500 W
velocity (u) = 20 m/s
Using P = Fυ
or, 500 = F x 20
= F =\(\frac {500}{20}\) = 25
F= 25 N

Question 5.
How is the power related to the speed at which a body can be lifted? How many kilogrims will a man working at the power of 100 W, be able to lift at constant speed of 1 mr1 vertically? (g = 10 ms^-2)
Answer:
We know that,

or, p = \(\frac {F.s}{t}\) P = Fυ = mg.υ [F = mg]
where, F = force
s = displacement
υ = velocity
t = time
Given,
power (P) = 100 W
velocity (υ) = 1 m/s
g = 10 m/s²
or, 100 = m x 10 x 1
∴ m = 10 kg

Question 6.
A car of mass 2000 kg is lifted up a distance of 30 m by a crane in 1 minute. A second crane does the same job in 2 minutes. What is the power applied by each crane?
Answer:
Given, mass of the car to be lifted, m = 2000 kg
height through which the car is to be lifted, h = 30 m
Time taken by first crane, t₁ = 1 minute = 60 s
time taken by second crane, t₁ = 2 minutes = 120 s
Amount of work done by each crane,
W = mgh = 2000 x 10 x 30 J
W= 6 x 10⁶ J
Power of first crane, ‘
P₁ = \(\frac{W_{1}}{t_{1}}=\frac{6 \times 10^{5} \mathrm{J}}{60 \mathrm{s}}\) = 10kW
Power of second crane
P₂ = \(\frac{W_{2}}{t_{2}}=\frac{6 \times 10^{5} \mathrm{J}}{120 \mathrm{s}}\) = 10kW

Question 7.
Calculate the electricity bill amount for a month of June, if 6 bulbs of 100 W for5 hours, 4 tube lights of 60 W for 5 hours, a TV of 50 W for 6 hours are used per day. The cost per unit is ₹ 5.
Answer:
Total energy used in a day = (6 x 100 x 5 + 4 x 60 x 5 + 1 x 50 x 6) Wh
= (3000+ 1200 +300)Wh = 4500 Wh
Total energy = 4.5 kWh = 4.5 unit
Total energy used in 30 days = 4.5 x 30 = 135 units
Bill amount = 135 units x ₹ 5 unit = ₹ 675.

Work, Power And Energy Class 9 Extra Questions Long Answer Type

Question 1.
State the conditions for positive, negative, and zero work. Give at least one example of each.
Answer:
1. Zero work: If the angle between force and displacement is 90°, then work done is said to be zero work.
Example: When a man carries a load on his head and moves on a level road. Work done by the man on the load is zero.

2. Positive work: Work done is said to be positive if the force applied on an object and displacement are in the same direction.
W = Fs

Example: Work done by the force of gravity on a falling body is positive.
3. Negative work: Work done is said to be negative if the applied force on an object and displacement is in opposite direction.
W = -Fs
Her displacement is taken to be negative (- s).

Example: Work done by friction force applied is negative on a moving body.

Question 2.
Give a reason for the following:
(a) A bullet is released on firing the pistol.
(b) An arrow moves forward when released from the stretched bow.
(c) Winding the spring of a toy car makes it to run on the ground.
(d) Falling water from a dam generates electricity.
(e) Winding the spring of our watch, the hands of the watch movement.
Answer:
(a) The chemical energy of gun powder is converted into kinetic energy of the bullet.
(b) The elastic potential energy in a stretched bow is converted into kinetic energy of the arrow.
(c) The potential energy of a spring is converted into kinetic energy of the toy.
(d) The kinetic energy of water is converted into electric energy.
(e) The potential energy of spring due to its windings is converted into mechanical energy of the watch.

Question 3.
State the law of conservation of energy. Show that the energy of a freely falling body is conserved.
Answer:
Energy can neither be created nor be destroyed, it can only be transformed ‘ m A from one form to another. The total energy before and after the transformation always remains constant.
Let us consider an object of mass ‘m’ dropped from a height h.
Total energy at point A

\(E_{T_{A}}=E_{K}+E_{P}\)
or, \(E_{T_{A}}=0+m g h\)
∴ \(E_{T_{A}}=m g h\)
Total energy at point B,
\(E_{T_{B}}=E_{T}+E_{p}\)
For finding out velocity at point B
apply υ² – u² = 2as
\(v_{\mathrm{B}}^{2}=2 g h\) = 2gh
Hence, \(E_{T_{B}}=\frac{1}{2} m \mathrm{V}_{\mathrm{B}}^{2}+m g\)
\(E_{T_{B}}=\frac{1}{2} m(2 g h)=m g h\)
Here, \(E_{T_{A}}=E_{T_{B}}\)
Hence if there is no energy loss, total energy is conserved.

Work, Power And Energy Class 9 Extra Questions HOTS

Question 1.
A running man has half the kinetic energy that a body of half of his mass has. The man speeds up by 1 m/s and then has the same kinetic energy as the boy. What are the original speeds of the man and the boy?
Answer:
Let us take
mass of boy = m
mass of man = M
velocity of boy = u
velocity of man = υ
Here, m = \(\frac {M}{2}\)
Initially
E_Kof man = \(\frac {1}{2}\) E_K of boy
\(\frac {1}{2}\) Mυ² = \(\frac {1}{2}\) mu² x \(\frac {1}{2}\)
and \(\frac {1}{2}\) Mυ² = \(\frac {1}{2}\) \(\frac{1}{2}\left(\frac{M}{2}\right) u^{2} \times \frac{1}{2}\)
∴ υ² = \(\frac{u^{2}}{4}\) ………….(1)

Finally
E_K of man = E_K of boy
\(\frac {1}{2}\)M(υ +1)² = \(\frac {1}{2}\) mu²
\(\frac {1}{2}\)M(υ +1)² = \(\frac{1}{2}\left(\frac{M}{2}\right) u^{2}\)
(υ +1)² = \(\frac{u^{2}}{2}\)
∴ υ +1 = \(\frac{u}{\sqrt{2}}\) …………(2)
υ = \({\sqrt{2}}\) + 1 = 2.41 m/s
and u = 4.82 m/s

Question 2.
Avinash can run with a speed of 8 m/s against the frictional force of 10 N, and Kapil can move with a speed of 3 m/s against the frictional force of 25 N. Who is more powerful and why?
Answer:
Power can be expressed as, P = Fu
Power of Avinash, P = Fu = 10 x 8 = 80 W
Power of Kapil, P = Fu = 25 x 3 = 75 W
Avinash is more powerful than Kapil.

Question 3.
The weight of a person on a planet A is about half that on the earth. He can jump up to 0.4 m height on the surface of the earth. How high can he can jump on planet A?
Answer:
For the case, of jump, the energy imparted by the person is converted into potential energy,
Hence,
(m_Ag_A)h_A = (m_eg_e)h_e ………(1)
Given, m_Ag_A = \(\frac{m_{e} g_{e}}{2}\) ………….(2)
Using (1) and (2),
\(\frac{h_{\mathrm{A}}}{2}=h_{e}\)
∴ h_A = 2h_e = 2 x 0.4 = 0.8m

Question 4.
A ball is dropped from a height of 10 m. If the energy of the bal] is reduced by 40% after striking the ground, how much high can the ball bounce back? (g 10 m/s²)
Answer:
Given,
height, h = 10
If the energy of the ball is reduced by 40%, the remaining energy of the ball is 60% of initial.
Hence ball will rebound to 60% of the initial height
h = \(\frac {60}{100}\) x 10 m
∴ h = 6m

Question 5.
Four men lift a 250 kg box to a height of 1 m and hold it. Without raising or lowering it
(a) How much work is done by men in lifting the box?
(b) How much work they do in just holding it?
Answer:
Given, mass of block, m = 250 kg
height, h = 1 m
(a) work done in lifting,
W = Fs = mgh = 250 x 10 x 1
W = 2500 J
(b) work done in holding, W = 0

Question 6.
What is power? How do you differentiate kilowatt from kilowatt-hour? The Jog falls in Karnataka state are nearly 20 m high. 2000 tonnes of water falls from it in a minute. Calculate the equivalent power if all this energy can be utilized. (g = 10 ms^-2)
Answer:
1. Power is rate of doing work.
2. Kilowatt is the unit of power and kilowatt-hour is unit of energy.
3. Given, height, h = 20 m
Mass per unit time,
m/t = 2000 tonnes per minutes = \(\frac{2000 \times 10^{3}}{60}\) kg/s
Power P = \(\frac{W}{t}=\frac{m g h}{t}=\frac{2000 \times 10^{3}}{60}\) = 10 x 20
∴ P = 6.67 x 10⁶ W = 6.67 MW

Question 7.
What happens to the kinetic energy when:
1.  the mass of the body is doubled at constant velocity?
2. the velocity of the body is doubled at constant mass?
3. the mass of the body is doubled but velocity is reduced to one fourth?
Answer:
1. The kinetic energy of body is given by,
E_k = \(\frac {1}{2}\) mυ⁶, E_k ∝ m. If the mass of the body is doubled its kinetic energy is also doubled.

2. Kinetic energy, E_k ∝ u²
If velocity of the body is doubled, its kinetic energy becomes four times.

3. Initial kinetic energy,
\(E_{K_{i}}\)= \(\frac {1}{2}\) mu²
Final kinetic energy,
\(E_{K_{f}}\) = \(\frac {1}{2}\)(2m) \(\left(\frac{v}{4}\right)^{2}=\frac{m v^{2}}{16}\)
Kinetic Energy becomes one eighth.

Question 8.
Why is the water at the bottom of a waterfall warmer than the water on the top?
Answer:
When waterfalls, its potential energy is converted into kinetic energy of molecules, and the kinetic energy of molecules is converted into heat energy.

Work, Power And Energy Class 9 Extra Questions Value Based (VBQs)

Question 1.
Aman is a student of class IX. He saw an old man trying to keep his box on the roof of a bus but was unable to do so. Aman picked up his box and placed the box on the roof of the bus.
The old man thanked Aman.
Answer the following questions based on the given paragraph:

• Is the work done by Aman while placing the box on the roof of the bus positive or negative?
• Is the work done by gravity on the box positive or negative?
• What values are shown by Aman?

Answer:

• Positive
• Negative
• Aman is a kind and helpful person.

Question 2.
In the winter season, John gifted an electric heater to his grandfather. The electric heater uses electricity to increase room temperature.
Answer the following questions based on the above paragraph:

• Write down the energy transformation in the electric heater.
• What values are shown by John?

Answer:

• Electric heater converts electricity into heat energy.
• John is an intelligent and caring person.

Question 3.
The government of a state decided to construct dams on the river for power generation. Nowadays the demand of electricity is continuously increasing and therefore more generation is required.
Answer the following questions based on the above paragraph:
(a) Write down the type of energy conversion is taking place in dams.
(b) Write down the values shown by the state government.
Answer:
(a) The potential energy of stored water is converted into electricity.
(b) The state government is working efficiently and showing good governance.

In this page, we are providing Force and Laws of Motion Class 9 Extra Questions and Answers Science Chapter 9 pdf download. NCERT Extra Questions for Class 9 Science Chapter 9 Force and Laws of Motion with Answers will help to score more marks in your CBSE Board Exams.

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

Extra Questions for Class 9 Science Chapter 9 Force and Laws of Motion with Answers Solutions

Force and Laws of Motion Class 9 Extra Questions Very Short Answer Type

Question 1.
Define the following terms

1. Force
2. Balanced forces
3. Unbalanced forces
4. Inertia
5. Momentum
6. Conservation of momentum.

Answer:

1. Force: It is an entity which when applied on a body changes or tends to change its state of motion and shape.
2. Balanced forces: When a number of forces acting simultaneously on a body do not bring about any change in the state of rest or of uniform motion along a straight line, then the forces acting on the body are said to be balanced.
3. Unbalanced forces: When a number of forces acting simultaneously on a body bring about a change in its state of rest or of uniform motion along a straight line, then these forces acting on the body are said to be unbalanced forces.
4. Inertia: Inertia is the natural tendency of an object to resist a change in its state of motion or rest.
5. Momentum: Momentum of a body is the product of its mass and velocity.
6. Conservation of momentum: In an isolated system, the total momentum remains conserved.

Question 2.
Name the physical quantity that measures inertia.
Answer:
Mass of body measures its inertia.

Question 3.
There are three solids made up of aluminum, steel, and wood, of the same shape and same volume. Which of them would have the highest inertia?
Answer:
Steel ball would have the highest inertia as steel is denser than the other two.

Question 4.
Name the factors on which the momentum of a body depends.
Answer:

• Mass and
• The velocity of the body.

Question 5.
Define one newton of force.
Answer:
Force is said to be 1 newton if it produces an acceleration of 1 rn/s² in a body of 1 kg.

Question 6.
An object is thrown vertically upwards. What is its momentum at the highest point?
Answer:
Since the velocity at the highest point is zero, so the momentum of the object is zero at the highest point.

Question 7.
State action and reaction when a bullet is fired from the gun.
Answer:
Action: Force exerted by a spring on the bullet.
Reaction: Force exerted on the gun.

Question 8.
An athlete runs some distance before taking a jump. Why?
Answer:
To gain momentum so that he may jump higher.

Question 9.
Mention any two effects of force.
Answer:

• It changes the state of rest or motion of a body.
• It changes the shape of the body.

Question 10.
What happens to the momentum of a body whose velocity is halved?
Answer:
The momentum of the body becomes half.

Question 11.
Give the magnitude and the direction of the net force acting on the cork of mass 10 g floating on water.
Answer:
Zero.

Question 12.
A car of mass 1000 kg is moving with velocity 5 m/s. Calculate the momentum of the car.
Answer:
Given, mass, m = 1000 kg
Velocity, u = 5 m/s
Momentum, P = mυ
P= 1000 x 5 = 5000kg m/s
P= 5000 kg m/s

Question 13.
A meteorite burns in the atmosphere before it reaches the Earth’s surface. What happens to the linear momentum?
Answer:
Meteorite burns due to heat produced by frictional force. The linear momentum of the meteorite decreases as a frictional force acts on it.

Question 14.
Find the acceleration produced by a force of 2000 N acting on a car of mass 800 kg.
Answer:
Given,
Mass, m =800kg
Force, F = 2000 N
Using F = ma
a = \(\frac{F}{m}\)
a = \(\frac{2000}{800}\) = 2.5 m/s²

Force and Laws of Motion Class 9 Extra Questions Short Answer Type 1

Question 1.
Write down SI unit of (i) force (ii) momentum.
Answer:

• newton (N)
• kg rn/s.

Question 2.
When a person hits a stone, his foot is injured. Why?
Answer:
When a person hits a stone, the stone exerts an equal force on his foot. Due to this force, his foot gets injured.

Question 3.
Why no force is required to move an object with a constant velocity?
Answer;
We know, F = ma
When, velocity is constant, then acceleration, a = 0. Hence, F = 0.

Question 4.
Why is it easier to catch a table tennis ball than a cricket ball, even both are moving with the same velocity?
Answer:
It is easier to catch a table tennis ball because the table tennis ball has less mass (inertia).

Question 5.
Write down the expression for the recoil velocity of the gun.
Answer:
Recoil velocity of gun is given by,
\(\mathrm{V}_{\mathrm{G}}=\frac{m_{b} v_{b}}{\mathrm{M}_{\mathrm{G}}}\)
m_b = mass of bullet
m_G = mass of gun
υ_b = velocity of bullet
V_G = recoil velocity of gun.

Force and Laws of Motion Class 9 Extra Questions Numericals

Question 6.
A car of mass 1000 kg moving with a velocity of 54 km/h hits a wall and comes to rest in 5 seconds. Find the force exerted by the car on the wall.
Answer:
Given, Mass = 1000 kg
Time = 5 s
Initial velocity, u = 54 km/h = 15 m/s
Final velocity, υ = 0 m/s
Time, t = 5s
using, F = m a
F = m\(\left(\frac{v-u}{t}\right)\) = 1000 \(\left(\frac{0-15}{5}\right)\) = -3000N

Question 7.
A body of mass 100g is at rest on a smooth surface. A force of 0.1-newton act on it for 5 seconds. Calculate the distance traveled by the body.
Answer:
Given, Mass of body = 100 g = 0.1 kg
Force, F = 0.1N
Time, t = 5s
Initial velocity, u = 0 m/s
Using formula, F = ma
⇒ a = \(\frac{F}{m}=\frac{0.1}{0.1}\) = 1 m/s²

Using formula, s = ut + at²
s = ut + \(\frac {1}{2}\)at²
⇒ s = 0 + \(\frac {1}{2}\) x 1 x (5)²
∴ s = 12.5 m

Question 8.
A bullet of mass 200 g is fired from a gun of mass 10 kg with a velocity of 100 m/s. Calculate the velocity of recoil.
Answer:
Given, Mass of bullet, m = 200 g = 0.2 kg
Massofgun, M = 10 kg
Velocity of bullet, V_b = 100 m/.s
Recoil velocity of gun, V_G = \(\frac{m v_{b}}{\mathrm{M}}\)
V_G = – \(\frac{0.2 \times 100}{10}\) = 2m/s
Recoil velocity of gun, V_G = 2 m/s

Question 9.
Two spheres of masses 20 g and 40 g moving in a straight line in the same direction with velocities of 3 mIs and 2 m/s respectively. They collide with each other and after the collision, the sphere of mass 20 g moves with a velocity of 2.5 miles. Find the velocity of the second ball after confusion.
Answer:
Given, m₁ = 20 g = 20 x 10^-3 kg
m₁ = 40g = 40g x 10^-3kg
u₁ = 3 m/s
u₂ = 2 m/s
υ₁ = 2.5 m/s
Applying conservation of linear momentum,
m₁u₁ + m₂u₂ = m₁υ₁ + m₂υ₂
20 x 10^-3 x 3 + 40 x 10^-3 x 2 = 20 x 10^-3 x 2.5 + 40 x 10^-3 x υ²
υ₂ = 2.25m/s.

Force and Laws of Motion Class 9 Extra Questions Short Answer Type 2

Question 1.
Newton’s first, second, and third law of motion.
Answer:
Newton’s first law of motion: An object remains in a state of rest or of uniform motion along a straight line unless compelled to change that state by an applied force.

Newton’s second law of motion: The second law of motion states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

Newton’s third law of motion: According to the third law of motion to every action, there is an equal opposite reaction and they act on two different bodies.

Question 2.
What is momentum? Write its SI unit. Interpret force in terms of momentum. Represent the following graphically.
(a) momentum versus velocity when mass is fixed.
(b) momentum versus mass when velocity is constant.
Answer:
Momentum gives an idea about the quantity of motion contained in a body.
The momentum of (P) of an object is defined as the product of its mass (m) and velocity (υ).
P = mυ
SI unit of momentum is kg ms^-1
Graphs
(a) If m = constant
P ∝ υ

(b) If v = constant
P ∝ m

Question 3.
“Action and reaction are equal and opposite but even they do not cancel each other.” Explain, why?
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. They act on two different bodies. Hence cannot cancel each other.

Question 4.
Why are the wheels of vehicles provided with mudguards?
Answer:
The rotating wheels of a vehicle throw out mud sticking to it tangentially due to the inertia of direction. The mudguards stop this mud to fall on another vehicle just moving behind the vehicle.

Question 5.
A car weighing 1600 kg moving with a velocity of 30 mIs retards uniformly coming to rest in 20 seconds. Calculate the
1. Initial and final momentum of the car.
2. Rate of change of linear momentum of the car.
3. Acceleration of the car.
Answer:
Given, mass, m = 1600 kg
Initial velocity, u = 30 m/s
Final velocity, υ = 0 m/s
Time, t = 20s
1. Initial momentum, P_i = mu = 1600 x 30
P_i = 4800 kg m/s
Final momentum, P_f = mυ = 1600 x 0
P_f = 0 kg m/s

2. Rate of change of linear momentum
= \(\frac{P_{f}-P_{i}}{t}\) = \(\frac{0-4800}{20}\) = – 240N
a = \(\frac{v-u}{t}\)

3.  Acceleration,
\(\frac{0 – 30}{20}\)
a = – 1.5 m/s².

Question 6.
Using the second law of motion, derive the relation between force and acceleration. A bullet of 10 g strikes a sand-bag at a speed of 10³ ms² and gets embedded after traveling 5 cm. Calculate
1. the resistive force exerted by the sand on the bullet.
2. the time is taken by the bullet to come to rest.
Answer:
According to the second law of motion,
The rate of change of momentum is directly proportional to the force applied.
F ∝ \(\frac{m(v-u)}{t}\)
F = \(\frac{km(v-u)}{t}\)
∴ F = kma
Take k = 1 in SI system
∴ F = ma

1. Given, mass of bullet, m = 10g = 10 x 10^-3kg
Initial velocity of the bullet, u = 10³m/s
Distance travelled by the bullet, s = 5 cm = 5 x 10^-2 m
Final velocity of the bullet = 0
Using the formula, υ^-2 – u^-2 = 2as
⇒ 0 – (10³)² = 2 x a x 5 x 10^-2

f = m x a = 10 x 10^-3 x (10⁷) = – 10⁵ N

2. From the formula,
υ = u + at
⇒  t = \(\frac {υ – u}{a}\) = \(\frac{0-10^{3}}{-10^{7}}\) = 10^-4 s = 0.0001 s

Question 7.
An object is placed on a rough surface. The external force of 20 N is acting on the body and 10 N frictional force is acting on the body.
Find
1. The net force on an object
2. Acceleration of an object if the mass of an object is 2 kg
3. The velocity of the object after 2 seconds if the object is started from rest.
Answer:
Given,

∴ υ = 10 m/s

Force and Laws of Motion Class 9 Extra Questions Long Answer Type

Question 1.
Explain why?
(a) A cricket player lowers his hands while catching the ball.
(b) The vehicles are fitted with shockers.
(c) A karate player breaks the pile of tiles or bricks with a single blow.
(d) In a high jump athletic event, the athletes are allowed to fall either on a sand bed or cushioned bed.
(e) In a moving car, the drivers and other passengers are advised to wear seat belts.
(f) China and glassware are packed with soft materials.
(g) Athletes are advised to come to a stop slowly after finishing a fast race.
Answer:
(a) 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.

(b) The vehicles are fitted with shockers (i.e., springs)
The floor of a vehicle is cónnected to the lower part of the vehicle by springs or shockers. When the vehicle moves over a rough road, the force due to jerks is transmitted to the floor of the vehicle through the shockers. The shockers increase the time of transmission of the force of jerk to reach the floor of the vehicle. Hence less force is experienced by the passengers in the vehicles.

(c) A karate player can break a pile of tiles with a single blow of his hand because he strikes the pile of tiles with his hand very fast, during which the entire linear momentum of the fast-moving hand is reduced to zero in a very short interval of time. This exerts a very large force on the pile of tiles which is sufficient to break them, by a single blow of his hand.

(d) In a high jump athletic event., the athletes are allowed to fall either on a sand bed or cushioned bed: This is done to increase the time of athletes fall to stop after making the high jump, which decreases the rate of change of linear momentum and decreases the impact.

(e) In a moving car, the drivers and other passengers are advised to wear seat belts: When brakes are applied sudden1y, the passengers of the car fall forward due to the inertia of motion. The seat belt worn by passengers of the car prevents them from falling forward suddenly. This enables the entire linear momentum of the passengers to reduce to zero over a long interval of time, hence it prevents injury.

(f) China and glassware are packed with soft material: China and glassware are wrapped in paper before packing to avoid breakage while transporting. During transportation, there may be collisions due to ta jerks of the packed wares. Soft material like paper slows down their rate of change of linear momentum. As a result, the impact is reduced and items are not broken.

(g) Athletes are advised to come to stop slowly after finishing a fast race: By doing so, he decreases the rate of change of linear momentum by increasing the time interval and hence, reducing the impact, which reduces injury.

Question 2.
Explain
(a) How do we swim?
(b) Why does a gun recoil?
(c) It is difficult to walk on sand or ice.
(d) The motion of rocket.
(e) Why does a fireman struggle to hold a hose-pipe?
(f) Rowing of a boat.
(g) When a man jumps out from a boat, the boat moves backward.
(h) Walking of a person.
Answer:
(a) While swimming, a swimmer pushes the water backward with his hands (i.e., he applies force in the backward direction, which is known as action.) The reaction offered by the water to the swimmer pushes him forward.

(b) Recoiling of a gun: When a bullet is fired from a gun, it exerts a forward force on the bullet and the bullet exerts an equal (in magnitude) and opposite (in direction) force on the gun. Due to the high mass of the gun, it moves a little distance backward and gives a backward jerk to the shoulder of the gunman.

(c) It is difficult to walk on sand or ice: When our feet press the sandy ground in the backward direction, the sand gets pushed away and as a result, we get only a small reaction (forward) from the sandy ground making it difficult to walk.

(d) Rocket propulsion Before firing the rocket, the total linear momentum of the system is zero because the rocket is in the state of rest. When it is fired, chemical fuels inside the rocket are burnt and the hot gases are passed through a nozzle with great speed. According to the law of conservation of linear momentum, the total linear momentum after firing must be equal to zero. As the hot gases gain linear momentum to the rear on leaving the rocket, the rocket acquires equal linear momentum in the upward i.e., opposite direction.

(c) A fireman has to make a great effort to hold a hose-pipe to throw a stream of water on the fire to extinguish it. This is because the stream of water rushing through the hose-pipe in the forward direction with a large speed exerts a large force on the hose-pipe in the backward direction which is known as the reaction force. This reaction force tends to move the hose-pipe in the backward direction. Therefore, a fireman struggles to hold the hose-pipe strongly to keep it at rest.

(f) Rowing of a boat: The boatman during the rowing of a boat pushes the water backward with oars (this is an action of the boatman). According to the third law of motion, water exerts an equal (in magnitude) and opposite (in direction) push on the boat which moves it forward (this is a reaction by water). Thus, harder the boatman pushes back the water with oars (i.e., greater is the action), greater is the reaction force exerted by water, and faster the boat moves in the forward direction.

(g) When a man jumps out from a boat, the boat moves backward: When the passengers start jumping out of a rowing boat, they push the boat backward with their feet. The boat exerts an equal (in magnitude) and opposite (in direction) force on passengers in the forward direction which enables them to move forward.

(h) 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 the action, According to Newton’s 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.

Force and Laws of Motion Class 9 Extra Questions HOTS

Question 1.
Two balls of the same size but of different materials, rubber and iron are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so, in which direction? Will they move with the same speed? Give reasons for your answer
Answer:
Yes, both the balls will start rolling in the direction opposite to the motion of the train. The speed of two balls will be different as the inertia of the two balls are different.

Question 2.
Two identical bullets are fired on by a light rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulders more and why?
Answer:
The light rifles will hurt more as the recoil velocity of the light rifle will be greater.

Question 3.
Velocity versus time graph of a ball of mass 50 g rolling on a concrete floor is shown in the figure. Calculate the acceleration and frictional force of the floor on the ball.

Answer:
Given, Mass of ball, m = 50 g = 50 x 10^-3 kg
Acceleration can be calculated by υ – t graph,

= \(\frac{80 \mathrm{m} / \mathrm{s}}{8 \mathrm{s}}\) = – 10 m/s²
a = – 10 m/s²
Friction force, F = ma
F = 50 x 10^-3 x 10
F = 0.5 N

Question 4.
A truck of mass M is moved under a force F. if the truck is then loaded with an object equal to the mass of the truck and the driving force is halved, then how does the acceleration change?
Answer:
Given, Initially
M₁ = M and F₁ = F
Finally
M₂ = 2M and F₂=\(\frac {F}{2}\)
Hence, a₁ = \(\frac{F_{1}}{M_{1}}\)
a₁ = \(\frac{F}{M}\)

and a₂ = \(\frac{F_{2}}{M_{2}}\)
a₂ = \(\frac{\mathrm{F}}{2 \times 2 \mathrm{M}}\) = \(\frac{F}{4M}\)
\(\frac{a_{1}}{a_{2}}=\frac{F / M}{F / 4 M}=4\)
a₂ = \(\frac{a_{1}}{4}\)
Acceleration will become one fourth.

Question 5.
Derive the unit of force using the second law of motion. A force of 5 N produces an acceleration of 8 ms^-2 on a mass m₁ and an acceleration of 24 ms^-2 on a mass m₂. What acceleration would the same force provide if both the masses are tied together?
Answer:
Given, Force, F = 5N
a₁ = 8 m/s²
and a₁ = 24 m/s²
From formula
m₁ = \(\frac{F}{a_{1}}\) = \(\frac{5}{8}\) kg
and m₂ = \(\frac{F}{a_{2}}\) = \(\frac{5}{24}\) kg
When both the masses tied together
a =\(\frac{\mathrm{F}}{m_{1}+m_{2}}\)
a = \(\frac{5}{\frac{5}{8}+\frac{5}{24}}\) = 6m/s²
a = 6m/s²

Force and Laws of Motion Class 9 Extra Questions Value Based (VBQs)

Question 1.
During a cricket match, a new player Ayush injured his hand while catching the ball. His friend Rudra advised him to catch the ball by lowering his hands backward. When Ayush got another chance to catch the ball, he successfully caught the ball without injuring his hands.
Answer the following questions:
(a) A cricket player lowers his hands while catching the ball. Explain why.
(b) Write down the values shown by Rudra.
Answer:
(a) If a player does not lower his hands while catching the ball, the time to stop the ball will be very small. So a large force has to 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 momentum of the ball. Therefore, the hands of the player are not injured.

(b) Rudra is a good person as he helped his friend Ayush. He is a knowledgeable person.

Question 2.
During servicing his bike Aman advised the mechanic to oil the shockers for its proper functioning.
Answer the following questions:
(a) The vehicles are fitted with shockers. Explain why.
(b) Write down the values shown by Aman.
Answer:
(a) The floor of a vehicle is connected to the lower part of the vehicle by springs or shockers. When a vehicle moves over a rough road, the force due to jerks is transmitted to the floor of the vehicle through the shockers. The shockers increase the time of transmission of the force of the jerk to reach the floor of the vehicle. Hence less force is experienced by the passengers in the vehicles.
(b) Aman is an intelligent and careful person.

Question 3.
Ranjan advised his son Ayush to wear a seat belt while driving the car.
Answer the following questions
(a) While driving the car, the drivers and other passengers are advised to wear seat belts. Explain why.
(b) Write down the values shown by Ranjan.
Answer:
(a) When brakes are applied suddenly, the passengers of the car fall forward due to the inertia of motion. The seat belt worn by passengers of the car prevents them from falling forward suddenly. This enables the entire linear momentum of the passengers to reduce to zero over a long interval of time, hence it prevents injury.
(b) Ranjan is a noble, intelligent, and careful person.