# NCERT Physics Class 11 Exemplar Ch 5 Laws of Motion Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 13. In Fig. a body A of mass m slides on plane inclined at angle to the horizontal and is the coefficient of friction between A and the plane. A is connected by a light string passing over a frictionless pulley to another body B, also of mass m, sliding on a frictionless plane inclined at angle to the horizontal. Which of the following statements are true? Blocks on Ramp

(a) A will never move up the plane.

(b) A will just start moving up the plane when

(c) For A to move up the plane, must always be greater than

(d) B will always slide down with constant speed.

Answer: (b) and (c)

Q. 14. Two billiard balls A and B, each of mass 50g and moving in opposite directions with speed of 5m s – 1 each, collide and rebound with the same speed. If the collision lasts for 10 – 3 s, which of the following statements are true?

(a) The impulse imparted to each ball is and the force on each ball is 250 N.

(b) The impulse imparted to each ball is and the force exerted on each ball is .

(c) The impulse imparted to each ball is 0.5 Ns.

(d) The impulse and the force on each ball are equal in magnitude and opposite in direction.

Answer: (c) and (d)

Q. 15. A body of mass 10kg is acted upon by two perpendicular forces, 6N and 8N. The resultant acceleration of the body is

(a) at an angle of 6N force.

(b) at an angle of 6N force.

(c) at an angle of 8N force.

(d) at an angle of 8N force.

Answer: (a) , (c)

## Very Short Answer

Q. 16. A girl riding a bicycle along a straight road with a speed of 5 m s – 1 throws a stone of mass 0.5 kg which has a speed of 15 m s – 1 with respect to the ground along her direction of motion. The mass of the girl and bicycle is 50 kg. Does the speed of the bicycle change after the stone is thrown? What is the change in speed, if so?

Answer: Yes, due to the principle of conservation of momentum.

Initial momentum =

Final momentum =

Q. 17. A person of mass stands on a weighing scale on a lift. If the lift is descending with a downward acceleration of , what would be the reading of the weighing scale?

Answer: Let R be the reading of the scale, in newtons.

Effective downward acceleration

(The weighing scale will show 5 kg) .

Q. 18. The position time graph of a body of mass 2 kg is as given in Fig. What is the impulse on the body at Distance Time Curve

Answer: Zero,