## MCQ Questions for Class 9 Science: Ch 11 Work and Energy 1. Work done by centripetal force is
(a) >0
(b) ≥0
(c) <0
(d) 0
► (d) 0

2. When a body falls freely towards the earth, then its total energy
(a) Decreases
(b) Increases
(c) First increases and then decreases
(d) Remains constant
► (d) Remains constant

3. If work is done at a faster rate, then
(a) power is more
(b) No power is required to do work
(c) power is less
(d) Infinite power is required
► (a) power is more

4. Moon revolves around the earth due to gravitational force (F) of earth on moon. The work done by the gravitational force is (r = radius of circular orbit of moon)
(a) F.2πr
(b) F.πr
(c) zero
(d) negative work
► (c) zero

5. Work done by a body is
(a) negative, positive or zero
(b) always positive
(c) always zero
(d) always negative
► (a) negative, positive or zero

6. 1 W. S = ________?
(a) 10 joule
(b) 1 joule
(c) 3.6 × 106 joule
(d) 2 joule
► (b) 1 joule

7. Scientifically, work is said to be done in which of the following cases
(a) Manish pulls the trolley for a certain distance
(b) Mira studies for her exam
(c) Manoj pushes the wall with no change in the position of wall
(d) Mira pulls the wall with no change in the position of wall
► (a) Manish pulls the trolley for a certain distance

8. P.E of a spring increases when it is in the state of
(a) compression
(b) neither a nor b
(c) expansion
(d) both a and b
► (d) both a and b

9. When speed of the moving object is doubled its
(a) Acceleration is doubled
(b) Momentum becomes four times more
(c) K E. is increased to four times
(d) Potential energy is increased
► (c) K E. is increased to four times

10. A ball is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy when its reaches the maximum height?
(a) Kinetic energy is double
(b) Kinetic energy is zero
(c) Kinetic energy is maximum at maximum height
(d) Kinetic energy is half of initial value
► (b) Kinetic energy is zero

11. A stone weighing 1 kg is dropped from rest from a height of 4 metres above the ground. When it has free-fallen 1 metre its total energy with respect to the ground is
(a) 15 J
(b) 40 J
(c) 20 J
(d) 30 J
► (b) 40 J

12. The energy possessed by an oscillating pendulum of a clock is
(a) kinetic energy
(b) potential energy
(c) restoring energy
(d) mechanical energy
►(d) mechanical energy

13. What is the commercial unit of energy?
(a) electron volt
(b) W/s
(c) kW h
(d) joule
► (c) kW h

14. Calculate the work done in moving a body of mass 50 Kg through a height of 5 m.(g = 10m/s2)​
(a) 250 J
(b) 2500 J
(c) 25 x 103 J
(d) 2.5 x 105 J
► (b) 2500 J

15. Find the correct statement
(a) 1 Gigawatt is equal to 109W
(b) power is the rate of doing work
(c) both a and b
(d) none of these
► (c) both a and b

16. If a force of F newton moves a body with constant speed v, the power delivered by it is
(a) F/v
(b) Fv
(c) F2v
(d) v/F
► (b) Fv

17. According to the law of conservation of energy
(a) Energy can’t be destroyed
(b) Energy can’t be created
(c) Energy can be transformed from one from to another
(d) All of the above
► (d) All of the above

18. In SI system, the unit of P.E. is
(a) erg
(b) dyne-cm
(c) J
(d) None of these
► (c) J

19. In the SI system, the unit of potential energy is
(a) newton
(b) joule
(c) watt
(d) metre per second
► (b) joule

20. Two bodies of equal weight are kept at heights of h and 1.5 A, respectively. The ratio of their PE is
(a) 3 : 2
(b) 2 : 3
(c) 1 : 1
(d) 4 : 3
► (b) 2 : 3

21.  On tripling the speed of motion of a body, the change in K.E. is
(a) 9 times
(b) 8 times
(c) 4 times
(d) 2 times
► (a) 9 times

22. A stone is tied to a string and whirled in a circular path. The work done by the stone is :
(a) negative
(b) zero
(c) positive
(d) none of the above
► (b) zero

23. 9800 joule of energy was spent to raise a mass of 50kg, the mass was raised to a height of
(a) 20m
(b) 980m
(c) 10m
(d) none of these
► (a) 20m

24. The linear momentum of a body of mass 2kg is 16kgms−1. What is its K. E?
(a) 64J
(b) 70J
(c) 60J
(d) none of these
► (a) 64J

25. Potential energy and kinetic energy are types of
(a) Electrical energy
(b) Magnetic energy
(c) Thermal energy
(d) Mechanical energy
► (d) Mechanical energy

26. A body of mass 5 kg is moving with an acceleration of 5 ms-2 gets a displacement of 2m, the work done by the force is:​
(a) 75 J
(b) 25 J
(c) 100 J
(d) 50 J
► (d) 50 J

27. Work done is said to be positive when a force causes displacement:
(a) In its own direction
(b) In the direction opposite to the applied force
(c) In the direction at right angles to the direction of applied force
(d) None of the above
► (a) In its own direction

28. Two masses m and 2m are dropped from certain height ‘h’. Then on reaching the ground,
(a) K.E. of them will be equal
(b) K.E. of the heavier is 4 times the K.E. of the lighter
(c) K.E. of the lighter is 4 times the K.E. of the heavier
(d) K.E. of the heavier is more than that of the lighter
► (d) K.E. of the heavier is more than that of the lighter

29. A rocket rises up in the air due to the force generated by the fuel. The work done by the:
(a) fuel is negative work and that of force of gravity is positive work
(b) fuel is positive work and that of force of gravity is negative work
(c) both fuel and force of gravity do positive work
(d) both fuel and force of gravity do negative work
► (b) fuel is positive work and that of force of gravity is negative work

30. A body is moved through a distance of 3 m in the following different ways. In which case is the maximum work done?
(a) when pushed over an inclined plane
(b) when lifted vertically upward
(c) when pushed over smooth rollers
(d) when pushed on a plain horizontal surface
► (b) when lifted vertically upward

31. In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of
(a) heat caused by the force of friction
(b) heat caused by the momentum
(c) heat caused by the motion
(d) heat flows from the blood to skin
► (a) heat caused by the force of friction

32. An electric lamp of 100w is used for 5 hours per day calculate the units of energy consumed by lamp in one day
(a) 1 unit
(b) 0.5 unit
(c) 1.5 units
(d) none of these
► (b) 0.5 unit

33. One unit of electricity is consumed by
A : P = 40 W bulb used for t = 25 hours
B : P = 20 W bulb used for t = 50 hours
Both A and B are true as, energy E in kWh is best related as
(a) E = Pt
(b) E = Pt/1000
(c) E = P/1000
(d) E = t/1000
► (b) E = Pt/1000

34. Work done by the gravitational force of earth on a satellite along a circular path is
(a) O
(b) minimum
(c) max
(d) all of these
► (a) O

35. In which case work is not done:
(a) A girl swimming in a pond
(b) A windmill lifting water from a well
(c) A standing man holding a suit case in his hand
(d) A sail boat moving in the direction of wind
► (c) A standing man holding a suit case in his hand

36. A boy holds a mass on his stretched hand. Then
(a) Work done against gravity is zero.
(b) Muscular energy is used
(c) Both (a) and (b)
(d) Neither (a) nor (b)
► (c) Both (a) and (b)