M.C.Q  : Work Power & Energy ( 1 to 1 0 )

LEVEL – I

1. Two bodies of masses m1 and m2 have equal momenta. Their kinetic energies E1 and E2 are in the ratio:

(A) √m1 : √m2

(B) m1 : m2

(C) m2 : m1

(D) m12 : m22

2. A chain of mass M, length l hangs from a pulley. If it is wound such that half of the chain remains overhung, the work done by the external agent is equal to

(A) Mgl/2

(B) (3/4)Mgl

(C ) (3/8)Mgl

(D) None of these

3. A block of mass m is suspended by a light thread from an elevator. The elevator is accelerating upward with uniform acceleration a. The work done during t secs by the tension in the thread is:

(A) (B) (C) (D) 0.

4. It is easier to draw up a wooden block along an inclined plane than to haul it vertically, principally because:

(A) the friction is reduced

(B) the mass becomes smaller

(C) only a part of the weight has to be overcome

(D) ‘g’ becomes smaller

5. A motor boat is travelling with a speed of 3.0 m/sec. If the force on it due to water flow is 500 N, the power of the boat is:

(A) 150 KW

(B) 15 KW

(C) 1.5 KW

(D) 150 W

6. Two masses of 1 gm and 4 gm are moving with equal kinetic energies. The ratio of the magnitudes of their linear momenta is:

(A) 4 : 1

(B) √2 : 1

(C) 1 : 2

(D) 1 : 16

7. A system of two bodies of masses m and M being interconnected by a spring of stiffness k moves towards a rigid wall with a K.E. E . If the body M sticks to the wall after the collision, the maximum compression of the spring will be (A) (B) (C) (D) 8. Two identical blocks each of mass m being interconnected by a light spring of stiffness k is pushed by a force F as shown in the figure. The maximum potential energy stored in the spring is equal to: (A) F2/2K

(B) F2/4K

(C) F2/8K

(D) None of these

9. A stone tied to a string of length l is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed u. The magnitude in its velocity as it reaches a position, where the string is horizontal, is

(A) (B) (C) (D) 10. A cord is used to raise a block of mass m vertically through a distance d at a constant downward acceleration g/4. The work done by the chord is

(A) mgd/4

(B) 3Mgd/4

(C) -3Mgd/4

(D) Mgd