CBSE Class 11 Laws of Motion Worksheet A

Law of Motion MCQ Questions with Answers Class 11 Physics Chapter 5

Question. When a body is stationary
(a) there is no force acting on it
(b) the forces acting on its are not in contact with it
(c) the combination of forces acting on it balance each other
(d) the body is in vacuum

Ans- (c)

Question.A force of 50 N is required topush a car on a level road with constant speed of 10 m/s. The mass of the car is 500 kg. What force should be applied to make the car accelerate at 1 m/s2?
(a) 550 N
(b) 450 N
(c) 500 N
(d) 2500 N

Ans- (a)

Question.A ship of mass 3 × 107 kg initially at rest is pulled by a force of 5 × 104 N through a distance of 3 m. Assuming that the resistance due to water is negligible, what will be the speed of the ship ?
(a) 0.1 m/s
(b) 1.5 m/s
(c) 5 m/s
(d) 0.2 m/s

Ans- (a)

Question.A constant force acts on a body of mass 0.9 kg at rest for 10 s. If the body moves a distance of 250 m, the magnitude of the force is
(a) 3 N
(b) 3.5 N
(c) 4 N
(d) 4.5 N

Ans- (d)

Question.In the above problem, if a push of 5 N is applied on the lighter mass, the force exerted by the lighter mass on the heavier mass will be
(a) 5 N
(b) 4 N
(c) 2 N
(d) None of the above

Ans- (d)

Question.In the above problem, the acceleration of the lighter mass will be
(a) 0.5ms ^-2
(b) 5/4 ms^-2
(c) 5/6 ms ^-2
(d) None of the above

Ans- (a)

Question.If a body loses half of its velocity on penetrating 3 cm in a wooden block, them how much will it penetrate more before coming to rest ?
(a) 1 cm
(b) 2 cm
(c) 3 cm
(d) 74 N

Ans- (a)

Question.In the game of tug of wars, a condition of equilibrium exists. Both the teams pull the rope with a force of 104N.The tension in the rope is
(a) 2 × 104 N
(b) 0
(c) 104 N
(d) none

Ans- (c)

Question. A 50 kg boy stands on a plateform spring scale in a lift that is going down with a constant speed 3 m/s. If the lift is brought to rest by a constant deceleration in a distance of 9 m, what does the scale read during this period ? (g = 9.8 m/s²)
(a) 500 N
(b) 465 N
(c) 515 N
(d) zero

Ans-(c)

Question. Ten coins are placed on top of each other on a horizontal table. If the mass of each coin is 10 g and acceleration due to gravity is 10 ms–2, what is the magnitude and direction of the force on the 7th coin (counted from the bottom) due to all the coins above it ?
(a) 0.3 N downwards
(b) 0.3 N upwards
(c) 0.7 N downwards
(d) 0.7 N upwards

Ans- (a)

Question. A sphere is accelerated upwards with the help of a cord whose breaking strength is five times its weight. The maximum acceleration with which the sphere can move up without cord breaking is
(a) 4g
(b) 3g
(c) 2g
(d) g

Ans- (a)

Question. A body of mass m is acted upon by a force F and the acceleration produced is a. If three forces each equal to F and inclined to each other at 120o act on the same body, the acceleration produced will be
(a) a√3
(b) 2a
(c) 3a
(d) zero

Ans- (d)

Question. An object is resting at the bottom of two strings which are inclined at an angle of 120° with each other. Each string can withstand a tension of 20 N. The maximum weight of the object that can be sustained without breaking the string is :
(a) 10 N
(b) 20 N
(c) 20 2 N
(d) 40 N

Ans- (b)

Question. A monkey is accelerating down a string whose breaking strength is two third of his weight. The minimum acceleration of the monkey should be
(a) 0
(b)2/3 g
(c) g
(d)g/3

Ans- (d)

Question. A lift weighing 1000 kg is moving upwards with an acceleration of 1 m/s². The tension in the supporting cable is
(a) 980 N
(b) 10800 N
(c) 9800 N
(d) 8800 N

Ans- (b)

Question. In an elevator moving vertically up with an acceleration ‘g’, the force exerted on the floor by a passenger of mass M is
(a) Mg
(b) 1/2 Mg
(c) zero
(d) 2 Mg

Ans-(d)

Question. The mass of a lift is 500 kg. What will be the tension in its cable when it is going up with an acceleration of 2.0 m/s² ?
(a) 5000 N
(b) 5600 N
(c) 5900 N
(d) 6200 N

Ans-(c)

Question. A man weighs 80 kg. He stands on a weighing scale in the lift, which is moving upwards with a uniform acceleration of 5 m/s². What would be the reading on the scale ? (g = 10 m/s²)
(a) Zero
(b) 400 N
(c) 800 N
(d) 1200 N

Ans-(d)

Question. In the above question normal reaction between ground and wedge will have magnitude equal to :
(a) N cos θ + Mg
(b) N cos θ + Mg + mg
(c) N cos θ – Mg
(d) N sin θ + Mg + mg

Ans-(a)

Question. A block is placed on the top of a smooth inclined plane of inclination θ kept on the floor of a lift. When the lift is descending with a retardation a, the block is released. The acceleration of the block relative to the incline is :
(a) g sin θ
(b) a sin θ
(c) (g –a) sin θ
(d) (g + a) sin θ

Ans-(d)

Question. A block of mass m is placed on a smooth wedge of inclination θ. The whole system is accelerated horizontally so that the block does not slip on the wedge. The force exerted by the wedge on the block (g is acceleration due to gravity) will be
(a) mg
(b) mg/cos θ
(c) mg cos θ
(d) mg sin θ

Ans-(b)

More questions- 

1. If force is acting on a moving body perpendicular to the direction of motion, then what will be its effect on the speed and direction of the body?

2. The two ends of spring – balance are pulled each by a force of 10kg.wt. What will be the reading of the balance?

3. A lift is accelerated upward. Will the apparent weight of a person inside the lift increase, decrease or remain the same relative to its real weight? If the lift is going with uniform speed, then?

4. A soda water bottle is falling freely. Will the bubbles of the gas rise in the water of the bottle?

5. Two billiard balls each of mass 0.05kg moving in opposite directions with speed 6m/s collide and rebound with the same speed. What is the impulse imparted to each ball due to other.

6. A nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei, the products must be emitted in opposite directions.

7. Explain why passengers are thrown forward form their seats when a speeding bus stops suddenly.

8. A man weighs 70kg. He stands on a weighting machine in a lift, which is moving (a) Upwards with a uniform speed of 10m/s.

(b) Downwards with a uniform acceleration of 5m/s².

(c) Upwards with a uniform acceleration of 5m/s2. Take g = 9.8m/s².

What would be the readings on the scales in each case what would be the reading if the lift mechanism failed and it came down freely under gravity?

9. (a) State impulse – momentum theorem?

(b) A ball of mass 0.1kg is thrown against a wall. It strikes the wall normally with a velocity of 30m/s and rebounds with a velocity of 20m/s. calculate the impulse of the force exerted by the ball on the wall.

10. Ten one rupee coins are put on top of one another on a table. Each coin has a mass m kg. Give the magnitude and direction of

(a) The force on the 7th coin (counted from the bottom) due to all coins above it.

(b) The force on the 7th coin by the eighth coin and

(c) The reaction of the sixth coin on the seventh coin.

Click on link below to download CBSE Class 11 Laws of Motion Worksheet A.