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2. Assertion : If the net external force on the body is zero, then its acceleration is zero. Reason : Acceleration does not depend on force.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is …

3. Assertion : Newton’s second law of motion gives the measurement of force. Reason : According to Newton’s second law of motion, force is directly proportional to the rate of change of momentum.

The gravitational force between two stones of mass 1 kg each separated by a distance of 1 metre in vacuum is

(a) Zero (b) 6.675×10-5 newton (c) 6.675×10-11 newton (d) 6.675×10-8 newton Answer: c (8)

7. Which of the following is the evidence to show that there must be a force acting on earth and directed towards the sun

(a) Deviation of the falling bodies towards east (b) Revolution of the earth round the sun (c) Phenomenon of day and night (d) Apparent motion of sun round the earth Answer: b (4)

The atmosphere is held to the earth by

(a) Winds (b) Gravity (c) Clouds (d) None of the above Answer: b (7)

A satellite of the earth is revolving in a circular orbit with a uniform speed v. If the gravitational force suddenly disappears, the satellite will

(a) Continue to move with velocity v along the original orbit (b) Move with a velocity v, tangentially to the original orbit (c) Fall down with increasing velocity (d) Ultimately come to rest somewhere on the original orbit Answer: b …

11. Figures I, II, III and IV depict variation of force with time

Ans. c (10)

6. If the distance between two masses is doubled, the gravitational attraction between them

(a) Is doubled (b) Becomes four times (c) Is reduced to half (d) Is reduced to a quarter Answer: d (10)

10. The variation of momentum with time of one of the body in a two body collision is shown in fig. The instantaneous force is maximum corresponding to point

(a) P (b) Q (c) R (d) S Ans. c (11)

8. A particle of mass m, initially at rest, is acted upon by a variable force F for a brief interval of time T. It begins to move with a velocity u after the force stops acting. F is shown in the graph as a function of time. The curve is a semicircle.

Ans. c (37)

47. Four particles each of mass m are placed at the corners of a square of side length l. The radius of gyration of the system about an axis perpendicular to the square and passing through its centre is

(a) l/ √2 (b) l/2 (c) l (d) (√2)l Ans. a (31)

48. The moment of inertia of a rod (length l, mass m) about an axis perpendicular to the length of the rod and passing through a point equidistant from its mid point and one end is

(a) ml2/12 (b) 7/48 ml2 (c) 13 ml2 (d) 19/48ml2 Ans. b (5)

6. Which of the following graph depicts spring constant k versus length l of the spring correctly

Ans. d (5)

7. A particle of mass m moving with velocity u makes an elastic one dimensional collision with a stationary particle of mass m. They are in contact for a very short time T. Their force of interaction increases from zero to F0 linearly in time T/2, and decreases linearly to zero in further time T/2. The magnitude of F0 is

(a) mu/T (b) 2mu / T (c) mu/ 2T (d) None of these ANS. b (5)

46. A wheel of mass 10 kg has a moment of inertia of 160 kg–m2 about its own axis, the radius of gyration will be

(a) 10 m (b) 8 m (c) 6 m (d) 4 m Ans. d (42)

45. Moment of inertia of a disc about its own axis is I. Its moment of inertia about a tangential axis in its plane is

(a) 5/2I (b) 3 I (c) 3/2 I (d) 2 I Ans. a (8)

Assertion : Soft steel can be made red hot by continued hammering on it, but hard steel cannot. Reason : Energy transfer in case of soft iron is large as in hard steel.

5. A body of 2 kg has an initial speed 5ms–1. A force acts on it for some time in the direction of motion. The force time graph is shown in figure. The final speed of the body.

Ans. c (9)

Assertion : Mountain roads rarely go straight up the slope. Reason : Slope of mountains are large therefore more chances of vehicle to slip from roads.

44. The moment of inertia of semicircular ring about its centre is

(a) MR2 (b) MR2/2 (c) MR2/4 (d) None of these Ans. a (7)

4. Figure shows the displacement of a particle going along the X-axis as a function of time. The force acting on the particle is zero in the region

(a) AB (b) BC (c) CD (d) DE ANS. a, c (22)

Assertion : A work done in moving a body over a closed loop is zero for every force in nature. Reason : Work done does not depend on nature of force.

43. A circular disc is to be made by using iron and aluminium, so that it acquires maximum moment of inertia about its geometrical axis. It is possible with

(a) Iron and aluminium layers in alternate order (b) Aluminium at interior and iron surrounding it (c) Iron at interior and aluminium surrounding it (d) Either (a) or (c) Ans. b (3)