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Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 2 - Work, Power and Energy [Latest edition]

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Chapters

(A) Force, Work, Power and Energy

    1: Forces: Turning Forces and Uniform Circular Motion

▶ 2: Work, Power and Energy

   Chapter 3: Machines

(B) Light

   Chapter 4: Refraction of Light

   Chapter 5: Electromagnetic Waves and Spectrum

(C) Sound

   Chapter 6: Sound

(D) Electricity and Magnetism

   Chapter 7: Electric Circuits, Resistance and Ohm's Law

   Chapter 8: Electric Energy, Power and Household Circuits

   Chapter 9: 1. Electromagnetism 2. Magnetic Effects of Electric Current 3. Electromagnetic Induction

(E) Heat

   Chapter 10: Calorimetry

(F) Modern Physics

   Chapter 11: Radioactivity

Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 2 - Work, Power and Energy - Shaalaa.com
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Solutions for Chapter 2: Work, Power and Energy

Below listed, you can find solutions for Chapter 2 of CISCE Goyal Brothers Prakashan for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १०.


EXERCISENUMERICAL PROBLEMS ON WORK, POWER AND ENERGY
EXERCISE [Pages 30 - 35]

Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० 2 Work, Power and Energy EXERCISE [Pages 30 - 35]

1. (a)Page 30
What do you mean by the term 'work'?
1. (b)Page 30

State two conditions for work to be done.

1. (c) (i)Page 30

State the mathematical expression for work, when a body is moving along horizontal plane.

1. (c) (ii)Page 30

State the mathematical expression for work, when a body is moving up an incline plane.

2. (a)Page 30

Name and define C.G.S. unit of work.

2. (b)Page 30

Name and define S.I. unit of work.

2. (c)Page 30

How is the S.I. unit of work related to C.G.S. unit of work?

3.Page 30

Why is the work done by a body zero, when a force acts at right angles to the direction of displacement?

4. (a)Page 30

A man climbs a slope and another walks a same distance on a horizontal level road. Who does more work? Give a reason for your answer.

4. (b) (i)Page 30

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A person walks on a levelled road.

4. (b) (ii)Page 30

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A person climbs a ladder.

4. (b) (iii)Page 30

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A car in neutral gear is coming down the slope.

5. (a)Page 30

In the following case, work is done or not done and why?

A group of boys pushing a thick wall.

5. (b)Page 30

In the following case, work is done or not done and why?

A porter carrying load on his head and climbing stairs.

5. (c)Page 30

In the following case, work is done or not done and why?

A porter carrying load on his head and walking along level road.

5. (d)Page 30

In the following case, work is done or not done and why?

A boy sitting on his chair and preparing his lesson.

5. (e)Page 30

In the following case, work is done or not done and why?

A girl swimming in a water tank.

5. (f)Page 30

In the following case, work is done or not done and why?

A man standing in a lift and going up to nth floor.

6. (a)Page 30

What is negative work?

6. (b)Page 30

Give two examples of negative work.

7. (a) (i)Page 30

Express erg in terms of mass, length and time.

7. (a) (ii)Page 30

Express joule in terms of mass, length and time.

7. (b)Page 30

What kind of work is done when the driver of a speeding car applies brakes?

8.Page 30

A force of 200 N acts on a body and displaces it 10 m. Calculate the work done by the force in S.I. units.

9.Page 30

What force should an engine develop, so that it causes a displacement of vehicle through 100 m, such that work done by it is 0.50 mega joule?

10.Page 30

A force of 1000 N is applied through a distance of 25 m while drawing a bucket of water from a well. Calculate the work done in joules.

11. (a)Page 30

Define power.

11. (b)Page 30

State two mathematical expressions for power.

12. (a) (i)Page 30

Define absolute unit of power in S.I. system.

12. (a) (ii)Page 30

Derive the mathematical formula for the S.I. unit of power in terms of mass, length, and time.

12. (b)Page 31

What is horse power stating clearly where it is used?

12. (c)Page 31

How many watts equal one horse power?

12. (d)Page 31

State two factors which determine power of a body.

12. (e)Page 31

Name two bigger units of power in S.I. system and state their magnitude in watt.

13. (a)Page 31

Differentiate between work and power.

13. (b)Page 31

Name two smaller units of power and state their magnitude.

14. (a)Page 31

What do you understand by the term energy?

14. (b) (i)Page 31

State the S.I. unit of energy.

14. (b) (ii)Page 31

State C.G.S. units of energy.

14. (c)Page 31

Differentiate between energy and power.

15. (a)Page 31
Define potential energy.
15. (b)Page 31

State the factors which determine the magnitude of potential energy.

15. (c)Page 31

Define elastic potential energy.

15. (d)Page 31

What is potential energy on the surface of earth?

16. (a)Page 31
State the law of conservation of energy.
16. (b)Page 31

Prove a freely swinging pendulum obeys law of conservation of energy.

17. (a)Page 31

What kind of energy is possessed by a body in the following case?

A stretched bow.

17. (b)Page 31

What kind of energy is possessed in a situation when?

A shooting arrow.

17. (c)Page 31

What kind of energy is possessed in a situation when?

Water stored in dams.

17. (d)Page 31

What kind of energy is possessed in a situation when?

A stone lying on the top of roof.

17. (e)Page 31

What kind of energy is possessed in a situation when?

A horse running along a level road

17. (f)Page 31

What kind of energy is possessed in a situation when?

An electron spinning around the nucleus.

18. (a)Page 31

Define kilowatt hour and convert it into joules.

18. (b)Page 31

Define electron volt and convert it into joules.

19. (a)Page 31

State the energy changes taking place in following case:

Switching on a flash light.

19. (b)Page 31

State the energy changes taking place in following case:

A car climbing on a steep hill road.

19. (c)Page 31

State the energy changes which take place when:

An air gun is loaded and then fired.

19. (d)Page 31

State the energy changes which take place when:

Water freezes in the freezing chamber of a fridge.

19. (e)Page 31

State the energy changes taking place in following case:

Exposure of a photographic film, while photographing.

19. (f)Page 31

State the energy changes taking place in following case:

Food consumed by human beings.

19. (g)Page 31

State the energy changes taking place in following case:

Burning of a strip of magnesium.

19. (h)Page 31

State the energy changes taking place in following case:

Water in a dam generates electricity.

19. (i)Page 31

State the energy changes taking place in following case:

A toy car is wound and then released.

19. (j)Page 31

State the energy changes taking place in following case:

Launching of a satellite by a rocket.

20. (a)Page 31

Give one example when:

Electric energy changes to potential energy.

20. (b)Page 31

Give one example when:

Potential energy changes to electric energy.

20. (c)Page 31

Give one example:

When magnetic energy changes into potential energy.

20. (d)Page 31

Give one example:

When electric energy changes into magnetic energy.

20. (e)Page 31

Give one example when:

Chemical energy changes to light energy.

20. (f)Page 31

Give one example when:

Light energy changes to chemical energy.

20. (g)Page 31

Give one example when:

Sound energy changes to electric energy.

20. (h)Page 31

Give one example when:

Electric energy changes to sound energy.

20. (i)Page 31

Give one example when:

Kinetic energy changes to heat energy.

20. (j)Page 31

Give one example when:

Heat energy changes to kinetic energy.

21. (a)Page 31

A machine raises a load of 750 N through a height of 16 m in 5 seconds. Calculate the power at which the machine works.

21. (b)Page 31

By what factor does the kinetic energy of a moving body change, when its speed is reduced by half?

21. (c)Page 31

What does the unit kilowatt hour measure? Define it.

22.Page 31

From the ground floor, a man comes up to the fourth floor of building using staircase. Another person comes up the same floor using elevator. Neglecting friction compare the work done in two cases.

23.Page 31

The power of a motor is 40 kW. At what speed can the motor raise a load of 20,000 N?

24. (a)Page 32

What energy changes are taking place in an oscillating pendulum?

24. (b)Page 32

Two objects A and B have masses in the ratio of 2 : 1 and are dropped from the same height.

  1. What is the ratio of their velocities on reaching ground?
  2. What is the ratio of their kinetic energy on reaching ground?
25. (a) (i)Page 32

Name two different units of energy (other than S.I. unit and its multiple).

25. (a) (ii)Page 32

A light and heavy mass has equal momentum. Which will have more kinetic energy and why?

25. (b)Page 32

A, B, C and D are four points on a hemispherical cup placed inverted on the ground. Diameter BC = 360 cm and AE = `R/3` (R is the radius of the cup). A small spherical mass of 500 g at rest at the point A slides down along the smooth surface of the cup. Assuming there is no loss of energy, calculate its:

  1. Potential Energy at A relative to B.
  2. Speed at point B (lowest point).
  3. Kinetic Energy at D (g = 10 ms−2).
26. (a)Page 32

What happens to the kinetic energy when mass of body is doubled at constant velocity?

26. (b)Page 32

What happens to the kinetic energy when velocity of body is doubled at constant mass?

26. (c)Page 32

What happens to the kinetic energy when mass of body is doubled, but velocity is reduced to half?

27.Page 32

A boy of mass 60 kg runs upstairs in 16 s and reaches 10 m high floor. Calculate:

  1. Force of gravity acting on the boy.
  2. Work done by the boy against the gravity.
  3. Power developed by the boy.
28. (a)Page 32

Name the quantity which is measured in eV.

28. (b) (i)Page 32

What will be the angle between force and displacement to attain minimum work?

28. (b) (ii)Page 32

What will be the angle between force and displacement to attain maximum work?

28. (c)Page 32

The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one.

29. (a)Page 32

State the amount of work done by an object when it moves in a circular path for one complete rotation. Give a reason to justify your answer.

29. (b)Page 32

Calculate the height through which a body of mass 0.5 kg is lifted if the energy spent in doing so is 1.0 J. Take g = 10 m s-2.

30. (a)Page 32

When an arrow is shot from a bow, it has kinetic energy in it. Explain briefly from where does it get its kinetic energy?

30. (b)Page 32

A stone of mass 50 g is thrown vertically upward from the ground with the initial velocity of 20.0 ms−1. Gravitational potential energy at ground level is considered zero. Apply the principle of conservation of energy to calculate the potential energy at the maximum height attained by stone. [g = 10 ms−1]

31.Page 32

6.4 kJ of energy causes a displacement of 64 m in a body in the direction of force in 2.5 seconds. Calculate:

  1. Applied force.
  2. Power in horse power [Take 1 HP = 750 W]
32. (a)Page 32

A toy car is acted upon by a force. State two conditions under which work done is zero.

32. (b)Page 32

A body of mass 50 kg has momentum 5000 kgms−1. Calculate

  1. Velocity of body
  2. Kinetic energy of body.
33. (a)Page 32

A body of mass 0.2 kg falls from a height of 10 m to a height of 6 m above the ground. Find the loss in potential energy taking place in the body. [g = 10ms−2]

33. (b)Page 32

A moving body weighing 400 N possesses 500 J of kinetic energy. Calculate the velocity with which the body is moving. (g = 10 ms2)

34. (a)Page 32

Abhay exerts a force of 150 N in pulling a cart with a constant speed of 10 ms−1. Calculate the power applied on cart.

34. (b)Page 32

Explain briefly why the work done by a fielder when he takes a catch in a cricket match is negative.

MULTIPLE CHOICE QUESTIONS Choose the most appropriate option.

1.Page 32

A boy drags a load 'L' along horizontal plane AB by applying a force F. The boy does:

  • no work

  • some positive work

  • negative work

  • none of these

2.Page 33

The SI unit of work is joule. It is expressed in terms of mass, length and time as:

  • kg m2s−3

  • kg m3s−2

  • kg2 m2s−2

  • kg m2s−2

3.Page 33

The SI unit of power is watt. It is expressed in terms of mass, length and time as:

  • kg m2s−3

  • kg m s−3

  • kg2 m2s−2

  • kg m s−2

4.Page 33

A stone resting on the roof of a building has:

  • potential energy

  • gravitational energy

  • kinetic energy

  • both potential energy and gravitational energy

5.Page 33

One horse power is equal to ______.

  • 1000 W

  • 500 W

  • 764 W

  • 746 W

  • 700 W

6.Page 33

One electron volt is equal to ______.

  • 1.6 × 10−17 J

  • 6.1 × 10−19 J

  • 1.6 × 10−19 J

  • 1.6 × 10−10 J

7.Page 33

Kilowatt hour is the commercial unit of ______.

  • electric power

  • electric energy

  • electric force

  • none of these

8.Page 33

Power is the product of ______.

  • force and velocity

  • force and displacement

  • force and acceleration

  • force and time

9.Page 33

The kinetic energy of a given body depends on the ______.

  • position

  • center of gravity of the body

  • momentum

  • displacement

10.Page 33

One kilocalorie is the amount of heat required to raise the temperature of:

  • one gram of water through 1°C

  • 1 kg of water through 100°C

  • one kg of water through 1°C

  • 1 kg of water through 10°C

11.Page 33

When a flash light is switched on the electric energy:

  • directly changes to light energy

  • first changes to light energy and then to heat energy

  • first changes to heat energy and then to light energy

  • none of the above

12.Page 33

A pendulum is swinging freely. The bob of pendulum has:

  • maximum K.E. at its extreme positions

  • minimum K.E. at its mean position

  • maximum K.E. at its mean position

  • both minimum and maximum K.E. at its mean position

13.Page 33

A pendulum is oscillating freely. Its bob has:

  • only kinetic energy

  • maximum kinetic energy at extreme position

  • maximum potential energy at its mean position

  • a constant energy, which is the sum of potential and kinetic energy

14.Page 33

A ball of mass m is dropped from height 'h'.

  • Potential energy of the ball at ground level is mgh.

  • Potential energy of the ball at height h is mgh.

  • kinetic energy of the ball at ground level is mgh.

  • Both potential energy of the ball at height h is mgh and kinetic energy of the ball at ground level is mgh.

15.Page 33

The factors which determine the work done by a body are:

  • There must be a force acting on body.

  • The force acting on the body must cause displacement in body.

  • The displacement of the body must be in the direction of applied force.

  • All of these

16.Page 33

No work is done if the force acting on a body is:

  • in the direction of displacement of body.

  • at some acute angle in the direction of displacement of body.

  • at right angles to the direction of displacement of body

  • none of these

17.Page 33

A stone whirled around in a circle with constant speed does:

  • maximum work

  • some work

  • no work

  • none of these

18.Page 34

In a stretched bow and arrow system, the arrow has:

  • translational kinetic energy

  • gravitational potential energy

  • elastic potential energy

  • all of these

19.Page 34

A body of mass 'm' is moving with a uniform velocity of 'v'. If the velocity increases three times the kinetic energy of the body will increase:

  • 3 times

  • 9 times

  • 6 times

  • not very certain

20.Page 34

A glass of boiling hot water cools down to room temperature. This process of cooling is known as:

  • waste of energy

  • dissipation of energy

  • losing of energy

  • destruction of energy

21.Page 34

During power production in a coal-based thermoelectric power plant, the correct sequence of energy conversions taking place is:

  • heat → mechanical → chemical

  • heat → mechanical → electrical

  • chemical → heat → light

  • heat → chemical → electrical

22.Page 34

One kilowatt hour is equal to:

  • 3,600 kJ

  • 3.6 MJ

  • 3,60000 J

  • both 3,600 kJ and 3.6 MJ

23.Page 34

A body of mass 0.2 kg falls from a height of 10 m to a height of 6 m above the ground level. If 'g' = 10 ms−2, the loss of gravitational potential energy is:

  • 8.0 J

  • 80.0 J

  • 0.8 J

  • 12 J

24.Page 34

A girl of mass 35 kg climbs from the first floor of a building at a height of 4 m above the ground to third floor at a height of 12 m above the ground. If 'g' is equal to 10 ms−2, the increase in gravitational potential energy of the girl is:

  • 1400 J

  • 2800 J

  • 4600 J

  • 4200 J

25.Page 34

A boy exerts a force of 150 N while pulling a hand cart at a speed of 3 ms−1. The power exerted by the body is:

  • 50 W

  • 150 W

  • 1500 W

  • 450 W

Direction for Q. Numbers 26 to 30: The questions given below are Assertion (A) and Reason (R) type questions. Choose the correct answer from options given below:

26.Page 34

Assertion (A): It is not necessary that a force always causes displacement of the body in its own direction.

Reason (R): The work done depends on (i) the magnitude of force, (ii) magnitude of displacement and (iii) the angle between the force and displacement.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion.

  • Both Assertion (A) and Reason (R) are true but Reason (R) is not the correction explanation of Assertion.

  • Assertion (A) is false, but Reason (R) is true.

  • Assertion (A) is true, but Reason (R) is false.

27.Page 34

Assertion (A): When a coolie walks on the horizontal ground while carrying a load on his head, no work is done against the force of gravity.

Reason (R): The coolie does work against the force of friction when he moves with load.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion.

  • Both Assertion (A) and Reason (R) are true but Reason (R) is not the correction explanation of Assertion.

  • Assertion (A) is false, but Reason (R) is true.

  • Assertion (A) is true, but Reason (R) is false.

28.Page 34

Assertion (A): A body capable of doing work is said to possess energy.

Reason (R): There is a transfer of energy if a body is acted upon by a force normal to the direction of displacement.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion.

  • Both Assertion (A) and Reason (R) are true but Reason (R) is not the correction explanation of Assertion.

  • Assertion (A) is false, but Reason (R) is true.

  • Assertion (A) is true, but Reason (R) is false.

29.Page 34

Assertion (A): In the uniform circular motion, the body is acted upon by a centripetal force, normal to displacement.

Reason (R): In the uniform circular motion, work done by the body is zero.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion.

  • Both Assertion (A) and Reason (R) are true but Reason (R) is not the correction explanation of Assertion.

  • Assertion (A) is false, but Reason (R) is true.

  • Assertion (A) is true, but Reason (R) is false.

30.Page 34

Assertion (A): In a polyatomic molecule, atoms can vibrate about their mean positions.

Reason (R): A polyatomic molecule has the vibrational energy in addition to rotational and translational energies.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion.

  • Both Assertion (A) and Reason (R) are true but Reason (R) is not the correction explanation of Assertion.

  • Assertion (A) is false, but Reason (R) is true.

  • Assertion (A) is true, but Reason (R) is false.

Complete the following by choosing the correct answers from brackets.

31. (a)Page 34

When a body vibrates about its mean position, the kinetic energy possessed by body is called ______ kinetic energy.

  • elastic

  • rotational

  • vibrational

31. (b)Page 34

One watt hour is equal to ______ J.

  • 3.6 × 106

  • 3.6 × 103

31. (c)Page 34

One electron volt (eV) is equal to ______ J.

  • 1.6 × 10−19

  • 1.6 × 10−21

31. (d)Page 34

Rate of doing work is called ______.

  • energy

  • power

31. (e)Page 34

The energy possessed by a stretched bow is ______.

  • gravitation potential energy

  • elastic potential energy

32.Page 35

Match the statements in Column A with those in Column B.

Column A Column B
(a) Law of conservation of energy. (i) Energy possessed by a body due to its position with respect to ground level.
(b) Kilowatt hour (ii) Energy possessed by an eagle flying high in sky.
(c) Kilocalorie (iii) Unit for buying or selling electric energy.
(d) Kinetic energy + Potential energy (iv) Energy cannot be created or destroyed and the sum total of energy in a system is constant.
(e) Gravitational potential energy. (v) Amount of energy required to raise the temperature of 1 kg of water through 1°C.
NUMERICAL PROBLEMS ON WORK, POWER AND ENERGY [Pages 35 - 40]

Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० 2 Work, Power and Energy NUMERICAL PROBLEMS ON WORK, POWER AND ENERGY [Pages 35 - 40]

1.Page 35

A boy of mass 55 kg runs up a flight of 40 stairs, each measuring 0.15 m in 15 s. Calculate

  1. Force acting on the boy.
  2. Work done by the boy.
  3. Gain of potential energy by the boy.
  4. Power developed by the boy.
  5. Horse power and power in kilowatts.

Practice Problems 1:

1.Page 35

A girl of mass 50 kg, climbs a flight of 100 stairs each measuring 0.25 m in height, in 20 s. Find

  1. Force acting on the girl
  2. Work done by the girl
  3. Gain in potential energy
  4. Power in (i) Watts (ii) Horse power.

[Take g = 10 ms−2; 1 HP = 750 W]

2.Page 35

A load of 220 kg is vertically pulled up by a crane through a vertical height of 16 m in 40 s. Calculate

  1. Force acting in the upward direction
  2. Total work done
  3. Horse power of the engine pulling the rope.

[Take g = 9.8 ms−2; 1 HP = 750 W]

2.Page 35

An energy of 4 kJ causes a displacement of 64 m in 2.5 s. Calculate

  1. Force
  2. Power

Practice Problems 2:

1.Page 36

A work of 1000 J is done on a body in 4 s, such that a displacement of 20 m is caused. Calculate

  1. Force
  2. Power
2.Page 36

What force must be applied to a body through a distance of 10 m, such that it does a work of 4000 J. If the mass of body is 20 kg, what is the acceleration of the body?

3.Page 36

An engine of power 200 W, operates for 4 s. Find the work done by the engine. If the force developed by the engine is 100 N, calculate the maximum displacement caused.

3.Page 36

Calculate the horse power of an engine, which lifts 4000 m3 of water from a depth of 50 m in 40 minutes.

[g = 10 ms−2, \[ \mathrm{D}_{\mathrm{H_{2}O}} \] = 103 kg m−3, 1 HP = 750 W]

Practice Problems 3:

1.Page 36

Calculate the horse power of the motor of an elevator, which can carry 10 persons of average mass 60 kg through a vertical height of 20 m in 30 s.

[Take g = 10 N/kg, 1 HP = 750 W]

2.Page 36

Calculate the power of an electric pump in horse power, which can lift 2000 m3 of water from a depth of 20 m in 25 minutes.

[Take g = 10 ms−2, 1 m3 of water = 103 kg and 1 HP = 750 W]

3.Page 36

Calculate the height through which a crane can lift a load of 4 t, when its motor of 4 HP operates for 10 s.

(Take g = 10 ms−2, 1 HP = 750 W)

4.Page 36

How long should an electric motor, of power 2 H.P. operate, so as to pump 5 m3 of water from a depth of 15m. [Take g = 10 N kg−1]

4.Page 36

An electric motor of power 200 W is switched on for 1 minute and 40 seconds. If 60% of the energy of the motor is useful, calculate

  1. useful work done by the motor
  2. load lifted by it through a vertical height of 10 m.

[g = 10 ms−2]

Practice Problems 4:

1.Page 37

An electric pump is 60% efficient and is rated 2 HP. Calculate the maximum amount of water it can lift through a height of 5 m in 40 s.

[Take g = 10 ms−2 and 1 HP = 750 W]

2.Page 37

Calculate the time for which a motor pump of 10 HP and efficiency 80% must be switched on, so as to pump 20 m3 of water through a vertical height of 20 m.

[Density of water = 1000 kg m−3; g = 10 ms−2; 1 HP = 750 W]

3.Page 37

In a hydroelectric power station, 1000 kg of water is allowed to drop through a height of 100 m in 1 sec. If the conversion of potential energy to electric energy is 60%. Calculate the power output. [Take: g = 10m/sec2]

5.Page 37

A bullet of an air gun weighs 0.01 kg. It is propelled out from the air gun with a velocity of 40 ms−1. Calculate the potential energy of the spring.

Practice Problems 5:

1.Page 37

A compressed spring is held near a small toy car of mass 0.15 kg. On the release of the spring, the toy car moves forward with a velocity of 10 ms−1. Find the potential energy of the spring.

2.Page 37

A catapult throws a stone of mass 0.10 kg with a velocity of 30 ms−1. If 25% of the P.E. of the elastic band is wasted during transmission, find the magnitude of the potential energy.

6.Page 37

A body of mass 4 kg is moving with a velocity of 4 ms−1. Find the ratio of its initial and final kinetic energy, if its mass is doubled and velocity is tripled.

Practice Problems 6:

1.Page 37

A body A of mass 20 kg is moving with a velocity of 1 ms−1. Another body B of mass 1 kg is moving with a velocity of 20 ms−1. Find the ratio of kinetic energy of A and B.

2.Page 37

A bullet of mass 0.2 kg, moving with a velocity of 200 ms−1, strikes a stationary wooden target of mass 5 kg. If all the energy is transferred to the wooden target, calculate the velocity with which the target moves in the forward direction.

7.Page 37

A body has a KE 'P'. If the mass of body increases 25 times, calculate its velocity, the kinetic energy remaining same.

Practice Problems 7:

1.Page 38

A body of mass (m) has a velocity (v). If the mass of the body increases 81 times, but the kinetic energy remains same, calculate the new velocity.

2.Page 38

A body P has KE (E). Another body Q, whose mass is 9 times than P, also has kinetic energy (E). Calculate the ratio of velocities of P and Q.

8.Page 38

A force of 20 N is required to pull up a body of mass 1.5 kg through a distance of 6 m along an inclined plane as shown in diagram alongside. Calculate

  1. Force of gravity acting on the body. (Take g = 10 ms−2)
  2. Work done by the force in pulling body along the inclined plane.
  3. Work done against the force due to gravity
  4. Account for the difference in answers (b) and (c).

Practice Problems 8:

1.Page 38

A force of 40 N is required to pull up cylindrical barrel of mass 2.5 kg through a distance of 7.5 m along the inclined plane as shown in diagram alongside. Calculate.

  1. Force of gravity acting on the barrel. (Take g = 10 ms−2)
  2. Work done by the force in pulling body along the inclined plane.
  3. Work done against the force of gravity.

2.Page 38

Adjacent diagram shows a body of mass 5 kg pulled up an inclined plane by a force of 30 N.

  1. Calculate force of gravity acting on body.  (Take g = 10 ms−2)
  2. Work done by the force in pulling body along the inclined plane.
  3. Work done against the force of gravity.

9.Page 38

A rickshaw puller exerts a force of 250 N in pulling rickshaw at a constant speed of 5 ms−1. Calculate the power developed by the rickshaw puller.

Practice Problems 9:

1.Page 39

A scooter develops a power of 1 HP while running at 36 km h−1. Calculate the force generated by its engine.

[Take 1 HP = 750 watts]

2.Page 39

The engine of a car develops a power of 5 HP and force 500 N while running a uniform speed S. Calculate the value of S.

10.Page 39

The heart of running athlete is beating 100 times a minute. If the work done by the heart per beat 1.2 J, calculate the power of the heart.

Practice Problems 10:

1.Page 39

The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one.

2.Page 39

The heart of a deer chased by a tiger beats 200 times in a minute and does a work of 1.4 joules per beat. What is the power of heart?

11.Page 39

An accelerated electron has an energy of 6.4 × 10−19 J. Express the energy of electron in electron volts (eV).

Practice Problems 11:

1.Page 39

A beam of electrons has an energy of 1 joule. How many electrons are in the beam?

[1 eV = 1.6 × 10−19 J]

2.Page 39

An accelerated electron has energy of 9.6 × 10−18 J. Express the energy in electron volts (eV).

12.Page 39

A body of momentum 10 kgms−1 and mass 0.05 kg. Calculate the kinetic energy of body.

Practice Problems 12:

1.Page 40

Calculate the kinetic energy of a body of mass 100 g and having a momentum of 20 kgms−1.

Solutions for 2: Work, Power and Energy

EXERCISENUMERICAL PROBLEMS ON WORK, POWER AND ENERGY
Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 2 - Work, Power and Energy - Shaalaa.com

Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 2 - Work, Power and Energy

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Concepts covered in अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 2 Work, Power and Energy are Work Done by the Force of Gravity (W = mgh), Forms of Energy > Solar Energy, Concept of Work, Measurement of Work, Concept of Power, Conversion of Potential Energy into Kinetic Energy, Conversion of Energies, Principle of Conservation of Energy, Proof: Kinetic + Potential Energy = Constant for Free Fall, Application of the Principle of Conservation of Energy, Expression for Work (W = F S cosθ), Mechanical Energy > Potential Energy (U), Concept of Energy, Mechanical Energy > Kinetic Energy (K), Forms of Energy > Heat Energy, Work vs Power, Energy vs Power, Potential vs Kinetic Energy, Forms of Energy > Light Energy, Forms of Energy > Chemical Energy, Forms of Energy > Hydro Energy, Forms of Energy > Electrical Energy, Forms of Energy > Nuclear Energy, Forms of Energy > Geo Thermal Energy, Forms of Energy > Wind Energy, Forms of Energy > Sound Energy, Forms of Energy > Magnetic Energy, Forms of Energy > Mechanical Energy.

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