# Class 9

Explore popular questions from Work and Energy for Class 9. This collection covers Work and Energy previous year Class 9 questions hand picked by experienced teachers.

## Mathematics

Work and Energy

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Q 1. A force of 20 N is acting on a body of mass 2 kg What is its acceleration?

A

2 {tex} m/s^2 {/tex}

B

40 {tex} m/s^2 {/tex}

C

22 {tex} m/s^2 {/tex}

10 {tex} m/s^2 {/tex}

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Q 2. Velocity of body changes from 3 m/s to 7 m/s in 2 seconds What is the acceleration which acted on the body

2 {tex} m/s^2 {/tex}

B

4 {tex} m/s^2 {/tex}

C

8 {tex} m/s^2 {/tex}

D

-2 {tex} m/s^2 {/tex}

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Q 3. A body of mass 20 kg is moving with a velocity of 45 m/s What is its momentum?

A

90 kg m/s

B

9 kg m/s

900 kg m/s

D

100 kg m/s

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Q 4. A body of mass 15 kg is moving with a velocity of 36 km/h It hits another body of mass 3 kg at rest The two bodies combine & move with velocity V What is the value of V in km/h

A

24

30

C

60

D

none

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Q 5. A body is dropped from a height of 80 m, it reaches to earths surface in:

4 sec

B

2 sec

C

16 sec

D

8 sec

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Q 6. Rate of change of momentum is equal to

force

B

impulse

C

acceleration

D

velocity

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Q 7. Rate of change of velocity is equal to

A

distance

B

displacement

C

force

acceleration

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Q 8. A body is moving in a circular path of radius 49 m It completes 1 revolution in 14 seconds The angular velocity is:

B

C

D

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Q 9. A body undergoes a displacement of 8 m when a force of 6N is applied The direction of force makes an angle of 60o with displacement The work done by the force on the body is-

24 J

B

24^3 J

C

48 J

D

24 75 J

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Q 10. If the angle between force F and displacement s is {tex} \mathrm 60^{o} {/tex}, then the work done is-

A

Fs

B

F/s

F - s

D

2Fs

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Q 11. A stone of mass falls freely through a vertical distance d, its kinetic energy is-

mgd

B

V ma2

C

mg/d

D

zero

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Q 12. Two bodies with kinetic energies in the ratio 4 : 1 are moving with equal liner momentum The ratio of their masses is

A

1 : 2

B

1 : 1

C

4 : 1

1 : 4

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Q 13. A mass of 12 kg at rest expleds into two pieces of masses 4 kg and 8 kg which move in opposite directions If the velocity of 8 kg piece is 6 m/s, then the kinetic energy of the other piece is (in joules)

A

64

B

128

C

144

288

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Q 14. The Power of a pump which can pump 200 kg of water to a height of 200 m in 10 s is (g = 10 {tex} m/s^2 {tex})

40 KW

B

80 KW

C

4000 KW

D

960 KW

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Q 15. A mass m falls freely rest The linear momentum after it has fallen through a height h is (g = acceleration due to gravity)

A

{tex}\sqrt{mgh}{/tex}

{tex}m\sqrt{2gh}{/tex}

C

{tex}m\sqrt{gh}{/tex}

D

zero

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Q 16. A body of mass m1 moving with a velocity 10 ms-1 collides with another body at rest of mass m2. After collision the Velocities of the two bodies are 2 ms-1 and 5 ms-1 respectively along the direction of motion of m1 m The ration is:{tex}\frac{m_{1}}{m_{2}}{/tex}

A

12

8

C

5

D

T

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Q 17. Two bodies, of equal masses along the same straight line with velocites + 3 m/s and - 5 m/s respectively, collide elastically Their velocities after the collision will be respectively:

0.3 m/s and - 0.5 m/s

B

- 0.4 m/s and 0.3

C

- 5 m/s and + 3 m/s

D

-0.3 m/s and 0.5 m/s

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Q 18. A bomb of mass m = 1 kg thrown vertically upwards with a speed u = 100 m/sec explodes into two parts after t = 5 sec A fargment of mass m1 = 400 gm moves downwards with a speed v1 = 25 m/sec, then speed v2 and direction of another mass m2 will be:

A

40 m/sec downwards

B

40 m/sec upwards

C

60 m/sec upwards

100 m/sec upwards

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Q 19. A mass of 20 kg moving with a speed of 10 m/s collides with another stationary mass of 5 kg As a result of the collision, the two masses stick together The kinetic energy of the composite mass will be:

A

600 joule

800 joule

C

1000 joule

D

1200 joule

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Q 20. The work done against gravity in taking 10 kg mass at 1 m height in 1 sec will be:

A

49 J

98 J

C

196 J

D

None of these

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Q 21. A heavy body moving with a velocity 20 ms-1 and another small object at rest undergo an elastic collision The latter will move with a velocity of:

A

20 m/s

40 m/s

C

60 m/s

D

zero

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Q 22. A gun of weight of 10 kg fires a shot of 0.5 g with a velocity 230 m/s Velocity of recoil gun is:

A

1.51 cm/sec

1.15 cm/sec

C

1.5 cmsec

D

1.10 cm /sec

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Q 23. A bullet of mass m and moving with velocity v is fired into a block of mass M and stick to it The final velocity would be:

A

coefficient of restitution = 0

B

coefficient of restitution = 1

coefficient of restitution = 9

D

coefficient of restitution < 1

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Q 24. The K.E. of a body of mass 2kg and momentum of 3Ns is:

1 J

B

2 J

C

3 J

D

4 J

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Q 25. A collision is said to be perfectly inelastic when :

coefficient of restitution = 0

B

coefficient of restitution = 1

C

coefficient of restitution = ¥

D

coefficient of restitution < 1