# Worksheet on work

Here under are the objective questions related to the work,energy and powers.Evaluate yourself by choosing the correct option.The answers are at the bottom of the worksheet.

1>A body at rest may here

(1) Speed

(2) Momentum

(3) Velocity

(4) Energy

2>A wound watch spring has

(1) Thermal energy

(2) Electrical energy

(3) Kinetic energy

(4) Potential energy

3>Water in a high dam possesses

(1) Thermal energy

(2) Electrical energy

(3) Kinetic energy

(4) Potential energy

4>A gas molecule at room temperature possesses

(1) Potential energy

(2) Kinetic energy

(3) Electrical energy

(4) No energy

5>Which one of the following possesses only kinetic energy

(1)    Bob of a pendulum at the extreme position.

(2)    Compressed spring

(3)     Bus moving up a hill

(4)    Cricket ball moving on the ground

6>Of the following the one possessing potential energy is

(1) An ideal gas molecule

(2) A bullet in flight

(3) Stretched rubber band

(4) A running boy

7>The work done on a body does not depend upon

(1) Displacement

(2) Force applied

(3) Angle between force and displacement

(4) Initial velocity of the body

8>The unit of work is

(1) Joule

(2) Newton

(3) Pascal

(4) Watt

9>Kilowatt hour is the unit of

(1) Power e

(2) Energy

(3) Force

(4) Time

10>If external force acting on a system is zero, then

(1) Its momentum remains constant.

(2) Its kinetic energy remains constant.

(3) Momentum and kinetic energy both remain constant.

(4) Neither momentum nor kinetic energy remains constant.

11>If external force is zero and the collision is elastic, then which of the following remains constant.

(1)Momentum only

(2) Kinetic energy only

(3) Momentum and kinetic energy both remain constant

(4)Neither momentum nor kinetic energy.

12>When two bodies stick together, the collision is said to be

(1) Perfectly elastic

(2) Perfectly inelastic

(3) Partially elastic

(4) Partially inelastic.

13>In a perfectly inelastic collision, the coefficient of restitution is

(1) 1

(2) 0

(3) 0.5

(4) more than 1

14>In a perfectly inelastic collision, the coefficient of restitution is

(1) 1

(2) 0

(3) 0.5

(4) Between 0 and 1.

15>A bent bow used for shooting an arrow possesses.

(1) Kinetic energy

(2) Potential energy

(3) Pressure energy

(4) Rest energy.

16>Two balls collide at the same temperature. Which of the -following is conserved.

(1) Velocity

(2) Momentum

(3) Temperature

(4) Kinetic energy

17>A man pushes a wall and fails to displace it. He does

(1)No work

(2) Maximum work

(3) Negative

(4) Positive work but not maximum

18>A coolie displaces a box from position A to position B on a horizontal rough surface. He then keeps the box at the same position A. The coolie does

(1) No  work

(2) Negative work

(3) Positive work

(4) Positive and negative works both

19>For the same kinetic energy, the momentum shall be maximum for

(1) An electron

(2) A proton

(3) A deuteron

(4) An $\alpha$ particle.

20>The kinetic energy acquired by a body of mass m after travelling a fixed distance from rest under the action of a constant force is

(1)    Directly proportional to m

(2) Inversely proportional to m

(3) Directly proportional to $\sqrt{m}$

(4) Independent of m.

21>When a body is moving in a horizontal circular path with a fixed speed, which one of the fol
lowing physical quantities remains constant.

(1)    Momentum of the body .

(2) Centripetal acceleration

(3) Kinetic energy of the body

(4) Displacement of the body from the centre of the circular path

22>A body of mass m is moving in a circle of radius r with constant speed v. The force on
the body is $\dfrac{mv^2}{r}$ and is directed towards the centre. What is the work done in moving the body over half the circumference of the circle?

(1) Zero

(2) $\dfrac{mv^2}{r} . \pi r$

(3) $\dfrac{mv^2}{r^2}$

(4) $\dfrac{mv^2}{r} .2r$

23>Two balls of different masses have the same kinetic energy. The ball having greater momentum will be

(1) lighter one

(2) heavier one

(3) both having equal mass

(4) sometimes lighter and sometimes heavier.

24>A car and a lorry are moving with the same kinetic energy. They are brought to rest by applying brakes which provide equal retarding forces. The distances covered by them before coming to rest will be

(1) equal

(2) directly proportional to their masses.

(3) inversely proportional to their masses

(4) inversely proportional to the square of their masses

25>The relation between kinetic energy K and linear momentum (p) of a moving body is

(1)    P = 2 Mk

(2) $p = \sqrt{2 m K}$

(3) $p = \dfrac{K^2}{2m}$

(4) $K = \dfrac{1}{2} mp$

26>A force F is applied on a body and it moves with a velocity v, the power will be

(1) Fv

(2) $\dfrac{F}{v}$

(3) $F v^2$

(4) $\dfrac{F}{v^2}$

27> A body is moved along a straight line by a machine delivering constant power. The distance moved by the body in time t is proportional to

(1) $t^{ \dfrac{1}{2}}$

(2) $t^{ \dfrac{3}{2}}$

(3) $t^{ \dfrac{3}{4}}$

(4) $t^2$

28>A mass of 3 g is moving with a velocity of 4 cm/s, the kinetic energy of the body is

(1) 24 J

(2) 2.4 J

(3) $24 \times 10^{-7}$ J

(4) $24 \times 10^{-7}$ J

29>A body of mass 5 kg possesses momentum 100 kg m/s. The kinetic energy of the body is

(1) 200 J

(2) 400 J

(3) 1000 J

(4) 2000 J

30>A car is moving along a straight horizontal road with velocity v. If the coefficient of friction between the tyres and the road is equal to m. The minimum distance required to stop the car is

(1) $\dfrac{v^2}{2 \mu g}$

(2) $\dfrac{v}{ \mu g}$

(3) $\dfrac{v^2}{2\mu g}$

(4) $\dfrac{v^2}{\mu }$

31>Tripling the speed of motor car multiplies the distance for stopping it by

(1) 3

(2) 6

(3) 9

(4) some other number.

32>A force 50 N acting on a panicle displaces it by 4 m at an angle 60°. What is the work done by the force

(1) 200 J

(2) 100 J

(3) 173 J

(4) Zero.

33> A uniform chain of length L and mass M lies on a smooth table and one-third of its length is hanging vertically down over the edge of the table. If g is acceleration due to gravity, to work required to pull the hanging part hack on the table is

(1) MgL

(2) $\dfrac{Mg L}{3}$

(3) $\dfrac{Mg L}{9}$

(4) $\dfrac{Mg L}{18}$

34>From a waterfall, water is pouring down at the rate of 100 kg/second on the blades of the turbine. If the height of the fall be 100 m, the time delivered to the turbine is approximately equal to

(1) 1 KW

(2) 10 KW

(3) 100 KW

(4) 1000 KW

35>The change in potential energy of the body when it is taken from the earth’s surface to a height nR above its surface is

(1) (n – 1 ) mgR

(2) $\dfrac{n}{n+1} mgR$

(3) n mgR

(4) $\dfrac{n}{n-1}mgR$

36>The potential energy of a certain spring when stretched through a distance ‘s’ is 10 J. The amount of work required to stretch this spring through an additional distance ‘s’ will be (in
Joules)

(1) 10

(2) 20

(3) 30

(4) 40

37>When a body moves with a constant speed around a circle, then

(1) No acceleration is produced in the body

(2) The velocity remains constant

(3) No force acts on the body

(4) No work is done on it

38>A particle of mass M is moving in a horizontal circle of radius R with uniform speed v. When it moves from one point to a diametrically opposite point, its

(1) kinetic energy changes by $\dfrac{mv^2}{4}$

(2) momentum does not change

(3) momentum changes by 2 mv

(4) kinetic energy changes by $mv^2$

39>A particle moves under the effect of a force F = Cx from x = 0 to $x_1$. The work done in
the process is

(1) $C {x_1}^2$

(2) $C^2 {x_1}$

(3) $\dfrac{1}{2}C {x_1}^2$

(4) Zero

40>A particle moves along X-axis from $x = x_1 \, to \, x = x_2$  under the influence of force given by F = 2x. The work done in this process is

(1) Zero

(2) $x \dfrac{2}{2} - x \dfrac{2}{1}$

(3) $2 x_2 ( x_1 - x_2 )$

(4) $2 x_1 ( x_1 - x_2 )$

41>The position dependent force F = $7 -2 x + 3 x^2$ N acts on a small body of mass 2 kg and displaces it from x = 0 to x = 5 m. The work done in Joules is

(1) 35

(2) 70

(3) 135

(4) 270

42>An engine develops 10 KW of power. How much time will it take to lift a mass of 200 kg to a height of 40 m.

(1) 4 s

(2) 5 s

(3) 8 s

(4) 10 s

43>A human heart pumps 75 $cm^3$ of blood per beat. The blood pressure is 100 mm of Hg. The beat frequency is 72 per minute. If g 9.80 $m/s^2$  and the density of Hg be $13.6 \times 10^3$, then the power of the heart is

(1) 0.012 W

(2) 0.12 W

(3) 1.2 W

(4) 12 W

44>A long spring is stretched by 2 cm, its potential energy is V. If the spring is stretched by 10 cm,
the potential energy stored in it will be

(1) $\dfrac{V}{5}$

(2) $\dfrac{V}{25}$

(3) 5 V

(4) 25V

45>A metallic wire of length L metre extends by I metre when stretched by suspending a weight
of Mg to it. Then the mechanical energy stored in the wire is

(1) Mgl

(2) $\dfrac{Mgl}{2}$

(3) $\dfrac{Mgl}{4}$

(4) 2 Mgl

46>Air expands from 100 litres to 300 litres at a constant pressure of 1 atm. The work done is

(1) $2 \times 10^4$ J

(2) $2 \times 10^5$ J

(3) 200 J

(4) $2 \times 10^7$

47>A cord is used to lower vertically a block of mass M through a distance s at a constant
downward acceleration of $\dfrac{g}{3}$. Then the work done by the cord on the block is

(1) $\dfrac{1}{3} Mgs$

(2) $\dfrac{2}{3} Mgs$

(3) $- Mgs$

(4) $- \dfrac{2}{3} Mgs$

48>A stone is released from a tower, its total mechanical energy during its fall

(1) increases

(2) decreases

(3) remains constant

(4) first increases and then becomes constant.

49>If the linear momentum of a body increases by 50%, the percentage increase in its KE will be

(1) 50%

(2) 100%

(3) 125 %

(4) 22.5 %

50>If the kinetic energy of a body increases by 50%, the percentage increase in linear momentum is

(1) 50%

(2) 22.5%

(3) 100%

(4) 125%

51>If the kinetic energy of a body is increased by 300%, the momentum of the body is increased
by

(1) 50%

(2) 100%

(3) 200%

(4) 300%

52>The variation of the force applied to a particle and the distance moved along a straight line is shown in the graph below, the kinetic energy of the particle at a distance of 3 m is (1) 6 J

(2) 4.5 J

(3) 3.25 J

(4) 2.75 J

53>The force applied on a horizontally moving cart of weight 5 kg is shown by the graph (a). The maximum height reached  by cart is (g = 10).

(1) 1 m

(2) 2 m

(3) 3 m

(4) 4 m

54>A 10.0 kg mass moves 3.0 m against a retarding force shown in fig. If the force is zero at the beginning, how much kinetic energy is changed. (1) 6 J

(2) -6 J

(3) 12 J

(4) -12 J

55>A rocket of mass m a fired from the surface of the earth of radius R. Then the increase in potential energy when it is at a height h above the surface of the earth is

(1) Mgh

(2) Mg ( R – h )

(3) $\dfrac{Mgh}{1 + \dfrac{h}{R}}$

(4) $\dfrac{MgR}{1 + \dfrac{R}{h}}$

56>A bullet fired into a target less half of its velocity after penetrating 30 cm. How much further will it penetrate before coming to rest.

(1) 10 cm

(2) 40 cm

(3) 60 cm

(4) 90 cm

57>Two balls A and B are of same mass. The ball A tied to a rigid thread and other B to a rubber cord. Both balls are initially deflected through 90° from vertical as shown. When the balls pass through the position of equilibrium the length of the rubber cord becomes equal to that of thread (fig). If $V_a \, V_b$  are the velocities of balls A and B, while passing through the point of equilibrium ,then it may be concluded (1) $V_a -= V_b$

(2) $V_a > V_b$

(3) $V_a < V_b$

(4) $V_a \geq V_b$

58>A meter stick of mass 800 g pivoted at one end and displaced through an angle of 60°.The increase in potential energy. (g = 10) (1) 2.0 J

(2) 4.0 J

(3) 20 J

(4) 0.20 J

59>A pendulum bob of mass 800 g is suspended from a thread 1 metre long. It is displaced
through on an angle 60° from vertical. The increase in potential energy of bob is (g = 10) (1) 2.0 J

(2) 4.0 J

(3) 20 J

(4) 0.20 J

60>A simple pendulum with a bob of mass m oscillates from A to C and back to A such that PB = H.If g is the acceleration due to gravity, then the velocity of the bob as it passes through B is (1) $\sqrt{5g H}$

(2) $\sqrt{2g H}$

(3) $\sqrt{g H}$

(4) zero

61>A bomb of 12 kg at rest explodes into two pieces of masses 4 kg and 6 kg. The velocity of 8 kg mass is 6 m/s. The kinetic energy of 4 kg mass

(1) 4m

(2) 1.6 m

(3) 3.2 m

(4) 6 m

62>A ball is dropped from a height of 10 m. If coefficient of restitution is 0.4. The ball rebounds to a height of

(1) 4 m

(2) 1.6 m

(3) 3.2 m

(4) 6 m

63>A ball strikes into a wall with a velocity of 10 m/s and bounces back with a velocity of 6 m/s. The coefficient of restitution is

(1) 1

(2) 0.4

(3) 0.6

(4) $\sqrt{0.6}$

64>A metal ball of mass 2 kg moving with a velocity of 36 km/h has a head on collision with a stationary ball of mass 3 kg. If after the collision the two balls move together, the loss in KE due to collision is

(1) 40 J

(2) 60 J

(3) 100 J

(4) 140 J

65>A heavy truck moving with velocity 60 km/h collides with a light drum at rest. If the collision be elastic, then the velocity of drum immediately after collision will be

(1) Zero

(2) 60 km/h

(3) 120 km/h

(4) Uncertain

66>A ball A is moving with velocity v. It strikes the ball B initially at rest. If the collision be elastic, then the velocities of balls A and B respectively immediately after collision will be (1)  v , 0

(2) $\dfrac{v}{2} , \dfrac{v}{2 }$

(3) 0 , v

(4) v , v

67>A blob of mud is moving with velocity v. It collides with a wall. If the collision be perfectly inelastic, the change in momentum of the blob will be

(1) mv

(2) 0

(3) -mv

(4) 2mv

68>A quartz ball is moving with a velocity v. It collides with a wall. If the collision be perfectly
elastic, the change in momentum of the ball will be

(1) mv

(2) 2mv

(3) -2mv

(4) Zero

69>A perfectly elastic ball A of mass m moving with velocity v collides elastically with the three identical stationary balls B, C and D and lying on a frictionless table (fig). The velocities of the four balls after collision respectively will be (1) v,0,0,v

(2) v,0, $\dfrac{v}{3}$ , 0

(3) v, $\dfrac{v}{3}$ , $\dfrac{v}{3}$ , $\dfrac{v}{3}$

(4) 0 ,0, 0, v

70>Six identical steel balls are lined up along a straight frictionlist groove at rest. Two similar balls moving with a speed v along the groove collide with this row from the extreme left (fig). Then after collision (1) all the balls will start moving to the right with speed $\dfrac{v}{4}$

(2) all the six balls initially at rest will move with speed $\dfrac{v}{6}$ and the two incident
balls will come to rest.

(3) two balls from the extreme right end will move with velocity v each to the right and the remaining balls will remain at rest

(4) one ball from the right will move on with speed 2v, all the remaining balls will be at rest.

71>A bullet of mass m, moving with velocity u strikes a suspended wooden block of mass M.
If the block rises to a height h, the initial velocity of the block will be (1) $\sqrt{2 g h}$

(2) $\dfrac{M + m}{m}\sqrt{2 g h}$

(3) $\dfrac{m}{M + m}\sqrt{2 g h}$

(4) $\dfrac{M + m}{m}\sqrt{2 g h}$

72>A body of mass m at rest explodes into 3 masses, 2 of which of mass $\dfrac{m}{4}$ each are thrown in perpendicular directions with velocities 3 m/s and 4 m/s respectively. The third piece will be thrown with a velocity

(1) 1.5 m/s

(2) 2.0 m/s

(3) 2.5 m/s

(4) 3.0 m/s

73> The power of a motor pump is 2 KW. If g = $10 m/s^2$, the amount of motor it can raise in 1minute to a height of 10 m is

(1) 100 litre

(2) 1000 litre

(3) 1200 litre

(4) 2000 litre

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