4 work and energy - the assam valley school today/worksheets/6/work a… · class-vi physics...

1Class-VI Physics Question Bank

4 WORK AND ENERGY

I. Tick ( ) the most appropriate answer.1. The SI unit of work is :

(a) newton (b) joule (c) metre (d) second2. Burning of wood is an example of conversion of :

(a) chemical energy to light and heat energy(b) mechanical energy to heat energy(c) heat energy to light energy(d) light energy to heat energy

3. When a brick is raised to a certain height, it gains :(a) potential energy (b) kinetic energy(c) wind energy (d) solar energy

4. Splitting of heavy unstable atom of uranium releases :(a) kinetic energy (b) nuclear energy(c) chemical energy (d) electrical energy

5. The ultimate source of all energy is :(a) petroleum (b) coal (c) sun (d) wind

6. If two teams play tug-of-war and both pull with equal force,then :(a) work is said to be done (b) no work is done(c) double work is done (d) none of these

7. Strong wind can turn the blades of a windmill because itpossesses :(a) potential energy (b) muscular energy(c) chemical energy (d) kinetic energy

8. Water cycle is caused due to :(a) chemical energy (b) solar energy(c) kinetic energy (d) potential energy

9. Water stored at a height in a dam possesses:(a) chemical energy (b) kinetic energy(c) potential energy (d) heat energy

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10. Work is said to be done if :(a) a body moves(b) a force is applied which brings about motion(c) a force is applied but no motion is produced(d) none of these

11. The work done by a body is the product of force and :(a) distance (b) speed (c) displacement (d) velocity

12. Burning of paper is an example of conversion of :(a) chemical energy into heat energy(b) chemical energy into heat and light energy(c) chemical energy into light energy(d) heat energy into light energy

13. Water stored in a tank on the top of roof has :(a) potential energy (b) kinetic energy(c) potential as well as kinetic energy (d) solar energy

14. Strong current of water turns the blades of turbine because itpossesses :(a) potential energy (b) kinetic energy(c) both potential and kinetic energy (d) none of these

15. Work is said to be done when :(a) force acts upon a body, but the body does not move(b) force acts upon a body and moves it in the direction of

force(c) force acts upon a body, but the body does not move in

the direction of applied force(d) none of these

16. If two boys push a table in opposite direction with equal force,then :(a) work is said to be done (b) no work is done(c) double work is done (d) none of these

17. When a person speaks in front of a microphone, the soundenergy is converted into :(a) loud sound energy (b) magnetic energy(c) chemical energy (d) electric energy


18. Two bodies A and B of equal masses having velocities in theratio 1 : 2, their kinetic energies are in the ratio :(a) 2 : 1 (b) 1 : 2 (c) 1 : 4 (d) 4 : 1

19. A device based upon conversion of light to electricity is :(a) electric heater (b) electric bulb(c) thermocouple (d) photocell

20. The work performed on an object does not depend upon :(a) applied force (b) displacement(c) initial velocity of the body (d) none of these

21. Food which we take converts :(a) potential energy to heat energy(b) electrical energy to heat energy(c) chemical energy to heat energy(d) none of these

22. Energy chain consists of :(a) solar energy (b) wind energy(c) fossil fuels (d) all the above

23. The S.I. unit of energy is :(a) newton (b) joule (c) pascal (d) second

24. The device which converts chemical energy to electrical energyis :(a) dry cell (b) electric heater(c) electric bulb (d) thermocouple

25. Potential energy of a person is minimum when :(a) person is standing (b) person is sitting on a chair(c) person is sitting on the ground(d) person is lying on the ground

Ans. 1. (b) 2. (a) 3. (a) 4. (b) 5. (a) 6. (b) 7. (d) 8. (b) 9. (c)10. (b) 11. (c) 12. (b) 13. (a) 14. (b) 15. (b) 16. (b) 17. (d)18. (c) 19. (d) 20. (c) 21. (d) 22. (d) 23. (b) 24. (a) 25. (d).

II. Fill in the blanks.1. Ability to do work is called ________ .2. When a force causes ________ in its own direction, the work

is said to be done.

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3. Work done by a body is the product of ________ anddisplacement.

4. One joule is the product of force of 1 N and displacement of________ .

5. Energy possessed by a body by virtue of its configuration or________ is called potential energy.

6. Energy possessed by a body by virture of its ________ iscalled kinetic energy.

7. In hydroelectric dams the ________ energy of flowing wateris transformed into electric energy.

8. When we speak in front of a microphone the sound energychanges into ________ energy.

9. Nuclear energy is released in the form of ________ energywhen the atom disintegrates.

10. During photosynthesis, the ________ energy changes tochemical energy.

11. Energy is defined as the ________ of doing work.12. The unit for the measurement of potential energy is ________ .13. Reading a book is a ________ work.14. Electricity produced from water is called ________ .15. Energy is measured by the amount of ________ that can be

done by that body.16. Wood has ________ energy stored in it.17. Sound energy is produced by ________ .18. When steam is used to turn turbines ________ is said to be

done.19. Scrap iron is separated from a heap of waste materials by using

big ________ fitted to a crane.20. Biogas is produced in ________ .21. The SI unit of energy is ________ .22. The kinetic energy of a body is by virtue of its ________ .23. Water cycle is caused due to ________ energy.24. Strong wind can turn the blades of a wind mill because it

possesses ________ energy.


25. Food which we take, converts to ________ energy.26. Wood has ________ energy stored in it.27. An electric bulb converts electric energy to ________ energy.28. ________ is the ultimate source of energy.29. If the mass of the body is doubled its potential energy will be

________ .30. A microphone converts ________ energy to ________

energy.Ans. 1. energy 2. displacement 3. force 4. 1 metre 5. position

6. motion 7. kinetic 8. electric 9. heat 10. light 11. capacity12. Joule 13. mental 14. hydroelectricity 15. work 16. chemical17. vibrations 18. work 19. magnet 20. biomass 21. joule22. motion 23. solar 24. kinetic 25. muscular 26. chemical27. light 28. Sun 29. doubled 30. sound, electrical.

III. Name the energy changes for each example in the list givenbelow.1. A loudspeaker 2. A Bunsen burner3. A microphone 4. An electric bell5. An electromagnet 6. An electric heater7. A transmitter 8. A radio set9. A dry cell 10. A burning fire cracker

Ans. 1. A loudspeaker: Electrical energy to sound energy.2. A Bunsen burner: Chemical energy to heat and light energy.3. A microphone: Sound energy to electric energy.4. An electric bell: Electric energy to sound energy.5. An electromagnet: Electric energy to magnetic energy.6. An electric heater: Electric energy to heat and light energy.7. A transmitter: Electrical energy to sound energy.8. A radio set: Electric energy to sound energy.9. A dry cell: Chemical energy to electrical energy.

10. A burning firecracker: Chemical energy to heat energy.IV. State whether the following statements are true or false (T/F):

1. Magnetic energy is always attractive in nature.

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2. The SI unit of energy is joule.3. A stretched bow and arrow system has kinetic energy.4. The energy possessed by an electric cell is chemical energy.5. During photosynthesis, the light energy changes into chemical

energy.6. An electric bulb converts electric energy into heat energy.7. The source of energy in a nuclear bomb is chemical energy.8. A freely falling stone possesses K.E. and P.E.9. In human body, the chemical energy of food changes into heat

energy.10. In hydroelectric stations, the potential energy of flowing water

changes into electric energy.Ans. 1. F 2. T 3. F 4. T 5. T 6. F 7. F 8. T 9. F 10. T.V. Statements given below are incorrect. Write the correct

statements.1. A running cat has potential energy.

Ans. A running cat has kinetic energy.2. A man is doing work when he is pushing a rigid wall by a huge

force.Ans. A man is not doing work when he is pushing a rigid wall by

a huge force.3. Moon is the ultimate source of energy.

Ans. Sun is the ultimate source of energy.4. Chemical energy is the cause of water cycle.

Ans. Solar energy is the cause of water cycle5. Loudspeaker converts sound energy to electrical energy.

Ans. Loudspeaker converts electrical energy to sound energy.6. A fire cracker converts mechanical energy to sound, light and

heat energy.Ans. A fire cracker converts chemical energy to sound, light and heat

energy.7. A falling stone converts kinetic energy to potential energy.

Ans. A falling stone converts potential energy to kinetic energy.8. The unit of work is newton.

Ans. The unit of work is joule.


9. A flowing river has potential energy.Ans. A flowing river has kinetic energy.

10. A parachutist has less potential energy when he is in the air thanwhen he is on the ground.

Ans. A parachutist has more potential energy when he is in the airthan when he is on the ground.

11. If two aeroplanes, one big and one small, travel at the samespeed, the smaller one has more kinetic energy.

Ans. If two aeroplanes, one big and one small, travel at the samespeed, the bigger one has more kinetic energy.

12. An electric bulb converts heat energy into light energy.Ans. An electric bulb converts electric energy into light energy.

13. Wind energy is the most powerful form of energy.Ans. Nuclear energy is the most powerful form of energy.

14. Biogas causes air pollution.Ans. Biogas does not cause air pollution.

15. Work is done when we hold a pile of books in our hands.Ans. Work is not done when we hold a pile of books in our hands.

16. Work done by a body is the product of pressure and displace-ment.

Ans. Work done by a body is the product of force and displacement.17. When electric current flows through a bulb, the electric energy

first changes into light energy and then heat energy.Ans. When electric current flows through a bulb, the electric energy

first changes into heat energy and then light energy.18. When we speak in front of a microphone the electric energy

changes into sound energy.Ans. When we speak in front of a microphone the sound energy

changes into electric energy.19. During photosynthesis heat energy changes into chemical

energy.Ans. During photosynthesis light energy changes into chemical

energy.20. In charging a car battery the chemical energy changes into

electric energy.

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Ans. In charging a car battery the electric energy changes intochemical energy.

21. A wound up spring of a watch possesses kinetic energy.Ans. A wound up spring of a watch possesses potential energy.

22. Nuclear energy is released in the form of light energy.Ans. Nuclear energy is released in the form of heat and light energy.

23. When a stone is projected vertically upwards its kinetic energychanges into potential energy.

Ans. When a stone is projected vertically upwards its potentialenergy changes into kinetic energy.

24. Kinetic energy of a body decreases with the increase in mass.Ans. Kinetic energy of a body increases with the increase in mass.

VI. Match the following:Column A Column B

1. Photosynthesis (a) Electrical energy → Magnetic energy2. Dry cell (b) Electrical energy → Sound energy3. Electromagnet (c) Solar energy → Chemical energy4. Door bell (d) Chemical energy → Electrical energy5. Electric heater (e) Electrical energy → Heat energy6. Table fan (f) Electrical energy → Light energy7. Photocell (g) Electrical energy → Mechanical energy8. Tubes and bulbs (h) Solar energy → Electrical energy9. The ringing of an (i) Kinetic energy → Sound energy

alarm clock10. A tin-can filled with (j) Chemical energy → Heat energy

stones is shaken and kinetic energy11. Rubbing your palms (k) Kinetic energy → Heat energy

together quickly12. The launching of a (l) Electrical energy → Mechanical energy

rocket13. The starting of an (m) Potential energy → Sound energy

electric fan


Ans. 1. (c) 2. (d) 3. (a) 4. (b) 5. (e) 6. (g) 7. (h) 8. (f) 9. (m)10. (i) 11. (k) 12. (j) 13. (l)

VII. Find the odd one out. Give a reason for your choice.1. Water stored in a tank, wound up spring watch, stretched

spring, speeding train.Ans. Speeding train: Speeding train possesses kinetic energy but

other have potential energy.2. A shooting star, a flying bird, blowing wind, a stone lying on

the top of roof.Ans. A stone lying on the top of roof: A stone lying on the top of

roof possesses potential energy but other possesses kineticenergy.

3. Coal, kerosene oil, petrol, solar cell.Ans. Solar cell: All except solar cell convert chemical energy to heat

energy. Solar cell converts solar energy to heat energy.4. Lifting a load, climbing a staircase, thinking, pulling a toy.

Ans. Thinking: Thinking is mental work but other are physicalworks.

5. Wound-up spring, stretched bow, stone lying on the roof,moving car.

Ans. Moving car: Moving car possesses kinetic energy but otherhave potential energy.

6. Coal, solar cooker, kerosene, wood.Ans. Solar cooker: Only solar cooker converts solar energy to heat

energy, whereas other convert chemical energy to heat energy.7. Diesel oil, firewood, kerosene, wind (in terms of longevity)

Ans. Wind: It is the only renewable source of energy.8. Diesel, petrol, kerosene, photocell.

Ans. Photocell: Only photocell converts light energy to electricalenergy. But burning of diesel, Petrol and kerosene convertchemical energy to heat energy.

9. Room heater, geyser, toaster, thermocouple.Ans. Thermocouple: Only thermocouple converts heat energy to

electrical energy. But other convert electric energy to heatenergy.

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10. Loudspeaker, microphone, electric bell, stereosystem.Ans. Microphone: Microphone converts sound energy to electrical

energy. But other three convert electrical energy to sound energy.VIII. Give reasons for the following:

1. Heat is a kind of energy.Ans. Heat is a kind of energy because it has the capacity of doing

work. The heat produced by burning coal, wood, oil or gas areutilised for cooking food. The steam produces from boilingwater is used in steam engine etc.

2. No work is done by a man rowing a boat upstream but is atrest with respect to the bank.

Ans. Work done = Force × displacement.When the man is rowing a boat upstream, it is at rest withrespect to the bank. So, the displacement of the boat is zero.Hence, no work is done by the boat.

3. A light and a heavy body can have equal kinetic energy.Ans. Kinetic Energy = ½ m v2.

A light and a heavy body can have equal kinetic energy if theyhave different velocities i.e. light body is moving with highspeed and heavy body is moving with low speed.

4. Light is a form of energy.Ans. Light is capable of doing work so it is a form of energy. It is

required for the process of photosynthesis in the green plants.It is also used in photographic plate, photocell etc.

5. Sun is the ultimate source of energy.Ans. Sun is the ultimate source of energy on the earth. Green plants

use sunlight during the process of photosynthesis and stored inthe form of chemical energy. It is used by other animals andhumans as food.Heat energy from sun causes wind. Wind energy can be usedin different ways. Sun light causes water cycle. Thus, sun is themain cause of all sources of energy.

6. No work is done if a person is pushing against a wall.Ans. Work done is given by product of force and displacement.


When a person is pushing against a wall with strong force, wallis not moving. So, displacement is zero. Hence, no work isdone by the person.

7. Hammer drives a nail into wood only when lifted and thenstruck.

Ans. Hammer drives a nail into wood only when lifted and thenstruck. Because when hammer is lifted, the potential energy ofhammer increases and it will drive the nail deeper.

8. Sound is a form of energy.Ans. Sound is a form of energy as it has capacity of doing work.

It can vibrate the eardrum and make hearing possible to us. Thestrong sounds of explosion shatter the glass panes of doorsand windows.

9. Solar cooker will be the means of cooking in the future.Ans. Solar cooker will be the means of cooking in the future.

Because solar cooker uses solar energy directly which isin exhaustible source of energy.

10. A horse and a dog are running with the same speed. The horsewill possess more kinetic energy.

Ans. A horse and a dog are running with the same speed. The horsewill possess more kinetic energy because the mass of horse is

more than the mass of the dog. And Kinetic energy = 12

mv2.

IX. Differentiate between:1. Reading and cooking (in terms of work done).

Ans. Reading and cooking: Reading is a mental work. But inphysics, no work is done in reading no matter if it needs energy.Cooking is an example of physical work.

2. Kinetic energy and potential energy.Ans. Kinetic energy and potential energy: Kinetic energy is the

energy possessed by the body by virtue of its motion, and K.E.= ½ mv2.

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Potential energy is the energy possessed by the body by virtueof its position, and P.E. = mgh.

3. Hydroelectricity and nuclear energy.Ans. Hydroelectricity and nuclear energy: Hydroelectricity is the

electricity produced by water. Nuclear energy is the energyderived from the nucleus of an atom.

X. Answer these questions.1. Define work. When is work said to be done?

Ans. Work is defined as the product of force and displacement.Work is said to be done, if a force acting on a body is ableto produce displacement in its own direction.

2. Is it possible that a force is acting on a body but still the workdone is zero? Explain by giving one example.

Ans. Yes. When a person is pushing against a wall, he is applyingforce but it does not produce any displacement. Hence workdone by the man is zero.

3. Define joule.Ans. One joule is equal to the work done when the point of

application of a force of 1N is displaced through a distance of1m in the direction of the force.

4. What are the two factors on which the amount of kinetic energydepends?

Ans. The kinetic energy depends on the following two factors.(i) Mass of the body, (ii) Speed of the body.

5. What are the two factors on which the amount of potentialenergy depends?

Ans. Two factors on which the amount of potential energy dependsare

(i) mass of the body, and(ii) height of the body above the ground.

6. State the principle of conservation of energy.Ans. The principle of conservation of energy states that the total

amount of energy in the universe always remains constant, that


is energy can neither be created nor destroyed, it can only bechanged from one form to another.

7. List four types of energies derived from the energy of the sun.Ans. Four types of energies derived from the energy of the sun are,

(i) chemical energy stored in plants(ii) wind energy (iii) energy of water

(iv) chemical energy in coal and petroleum.8. How is hydroelectricity produced?

Ans. River water is stored in reservoirs in the dam. When the storedwater is made to flow through special channels, the potentialenergy of water changes into kinetic energy. The kinetic energyof flowing water is utilised in rotating the blades of the turbine.The K.E. of the rotating turbine is converted into electricalenergy by a generator. Thus hydroelectricity is produced.

9. Biogas plants are a boon to the villagers. Explain why.Ans. Biogas plants are a boon to the villagers because biogas is a

cheap and clean fuel. It does not produce smoke or cause airpollution. Biogas is used as a fuel for cooking and as anilluminant for street lighting.

10. How is petroleum formed?Ans. When dead remains of sea animals and plants got buried

millions of years ago, because of high temperature and highpressure under the earth, they slowly changed to formpetroleum.

11. What is biogas? Name its main constituents.Ans. Biogas is the gas produced from biomass consists of dried

leaves, cowdung or any other non-usable products of plant andanimal origin.Its main constituents are methane (65%), carbon dioxide andhydrogen.

12. What will happen to the kinetic energy of the body (when itsvelocity remains the same), if(a) the mass of the body is doubled?(b) the mass of the body is halved?

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Ans. When the velocity of the body remains the same(i) the kinetic energy of the body will be doubled if the mass

of the body is doubled.(ii) the kinetic energy of the body will be halved if the mass

of the body is halved.13. What will happen to the kinetic energy of the body (when mass

of the body remains the same), if(a) its velocity is doubled? (b) its velocity is halved?

Ans. When mass of the body remains the same(a) the kinetic energy will increased four times if its velocity

is doubled.(b) the kinetic energy will decreased to one fourth if its

velocity is halved.14. What will happen to the potential energy of the body (when the

height is kept the same), if(a) the mass of the body is doubled?(b) the mass of the body is halved?

Ans. When the height is kept the same(a) the potential energy of the body will be doubl if the mass

of the body is doubled.(b) the potential energy of the body will be halved if the mass

of the body is halved.15. What will happen to the potential energy of the body (when its

mass is kept the same), if(a) the body is raised to double the original height?(b) the body is lowered to half the original height?

Ans. When its mass is kept the same(a) the potential energy of the body will be doubled if the

body is raised to double the original height.(b) the potential energy of the body will be halved if the body

is lowered to half the original height.16. A person holding a suitcase is at rest. Is he doing any work?

Ans. No. The person is not doing any work when he is holding asuitcase and is at rest as in this case displacement is zero.


17. What is the amount of work done by a man pushing a rigid wallwith a force of 200 N?

Ans. The work done by a man pushing a rigid wall with a force of200 N is zero as there is no displacement.

18. How do you define energy?Ans. Energy is the capacity or ability of a body to do work.

19. What do you understand by the term kinetic energy andpotential energy?

Ans. Kinetic energy is the energy possessed by a body by virtue ofits motion.Potential energy is the energy possessed by a body by virtueof its position.

20. How does the kinetic energy of a body changes if(i) its mass is doubled. (ii) velocity is doubled?

Ans. (i) If the mass of a body is doubled, then kinetic energy ofthe body will be doubled.

(ii) If the velocity is doubled, the kinetic energy of the bodywill become four times of the original value.

21. State two factors which determine the work done by a body.Ans. Two factors which determine the work done by a body are

(i) the applied force, and(ii) the displacement of the body in the direction of the force.

22. What is biomass?Ans. Biomass mainly consists of dry leaves, cowdung or any

unwanted product of plant and animal origin.23. How work and energy are related to each other?

Ans. The energy of a body is equal to the amount of work done byit when its energy is released. If a body does not have energy,it cannot do any work. Whenever a body does work, an equalamount of its energy is used up.

24. Name two basic kinds of energy.Ans. Two basic kinds of energy are:

(i) Kinetic energy and (ii) Potential energy.

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25. (a) What do you understand by the term work?(b) State a situation in which force is applied on a body, but

no work is done.(c) Write the mathematical expression for work.

Ans. (a) When a force causes displacement in its own direction,work is said to be done.

(b) If the force applied does not produce any displacement ofa body then no work is done.For example, if we push a wall and it does not move, thenno work is done, no matter how much energy we havespent.

(c) The mathematical expression for work isWork done = Force × Displacement through which

force act W = F × S.

26. (a) Give four examples of kinetic energy.(b) Two bodies have equal mass. However, speed of one

body is double than that of the other. Which of the twobodies has more kinetic energy?

Ans. (a) Four examples of kinetic energy are(i) a running train, (ii) a speeding car,

(iii) a strong wind, and (iv) a stone rolling down a hill(b) The body which has double speed has more kinetic

energy.27. Give three examples of potential energy.

Ans. Three examples of potential energy are:(i) When the rubber sling of a catapult is stretched, the

muscular energy is stored in rubber.(ii) The compressed string of a toy pistol, and(iii) The wind up spring of an alarm clock.

28. State the kind of energy (potential energy or kinetic energy)possessed by the following.(a) A stone resting at the top of hill.


(b) An arrow shooting from a bow.(c) A flying mosquito.(d) A wound up spring of a toy car.(e) A speeding car.(f) A bullet fired from a gun.

Ans. (a) A stone resting at the top of hill — Potential energy(b) An arrow shooting from a bow — Kinetic energy(c) A flying mosquito — Kinetic energy(d) A wound up spring of a toy car — Potential energy(e) A speeding car — Kinetic energy(f) A bullet fired from a gun — Kinetic energy

XI. Numerical Problems.1. How much work is done in raising a stone of mass 5 kg to a

height of 5 metre? (g = 10 m/s2)Ans. Mass = 5 kg

... Force = 5 × 10 = 50 N [... g = 10 m/s2]Displacement = 5 m

Work done = Force × displacement= 50 N × 5 m= 250 J.

2. A force of 25 N acts on a body of mass 5 kg and producesa displacement of 5 m in its own direction. Calculate the amountof work done.

Ans. Force = 25 NDisplacement = 5 m

The required work done = Force × Displacement= 25 N × 5 m = 125 J.

3. A bullet of mass 100 g, is moving with a speed of 200 ms–1.What is its kinetic energy?

Ans. Mass, m = 100 g = 1

10 kg

Speed, v = 200 ms–1

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... The required kinetic energy = mv2

= × (200)2

=120 × 40000

= 2000 J.4. How fast does a man, weighing 60 kg run so that his kinetic

energy is 750 J ?Ans. Kinetic energy (K.E.) = 750 J.

Mass of man (M) = 60 kgVelocity of man (V) = ?

... K.E. = mv2

⇒ 750 = × 60 × v2

⇒ 25 = v2

... v = 5 m/s.

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4 work and energy - the assam valley school today/worksheets/6/work a… · class-vi physics...

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