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Class 11 Physics MCQ Questions of Laws of Motion with Answers?

Answer 1

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Check the below MCQ Questions for class 11 Physics Laws of Motion with Answers: - 
 

Practice MCQ Questions for class 11 Physics Chapter-Wise

1. The mass of a body which is equal to the ratio of the force acting on a body to the acceleration produced in the body is

(a) the gravitational mass
(b) the electromagnetic mass
(c) the internal mass
(d) the inertial mass

2. The force required to produce an acceleration of 2 m/s² on a mass of 2 kg is

(a) 4 N
(b) 10 N
(c) 22 N
(d) 18 N

3. A machine gun fires a bullet of mass 40 g with a velocity of 1200 ms^-1. The man holding it can exert a maximum force on 144 N on the gum. How many bullets can he fire per second at the most?

(a) one
(b) four
(c) two
(d) three

4. A passenger in a moving bus is thrown forward when the bus is suddenly stopped. This is explained

(a) by Newtons first law
(b) by Newtons second law
(c) by Newtons third law
(d) by the principle of conservation of momentum

5. A body of mass 5 kg is travelling with a uniform velocity of 2 m/s. Its momentum is

(a) 10 kg m/s
(b) 7 kg m/s
(c) 2 .5 kg m/s
(d) 3 kg m/s

6. Inside the nucleus, two protons are held together by a force which overcomes the repulsion. This force is called

(a) gravitational force
(b) electrostatic force
(c) weak force
(d) strong force

7. A block of wood is placed on a surface. A force is applied parallel to the surface to move the body. The frictional force developed acts

(a) normal to the surface upwards
(b) normal to the surface downwards
(c) along the direction of the applied force
(d) opposite to the direction of the applied force

8. A block of wood is placed on a surface. A force is applied parallel to the surface to move the body. The frictional force developed acts

(a) normal to the surface upwards
(b) normal to the surface downwards
(c) along the direction of the applied force
(d) opposite to the direction of the applied force

9. Out of the basic forces, gravitational force

(a) ranks first in strength
(b) ranks second in strength
(c) ranks third in strength
(d) ranks fourth in strength

10. A reference frame attached to the earth

(a) is an inertial frame by definition
(b) cannot be an inertial frame because the earth is revolving round the sun
(c) cannot be an inertial frame because the earth is rotating about its own axis
(d) both b and d 

11. Newton's first law of motion describes the

(a) inertia
(b) energy
(c) work
(d) moment of inertia

12. Inertia is that property of a body by virtue of which the body is

(a) Unable to change by itself the state of uniform motion
(b) Unable to change by itself the state of rest and or uniform linear motion
(c) Unable to change by itself the state of rest
(d) Unable to change by itself the direction if motion

13. Physical independence of force is a consequence of

(a) third law of motion
(b) second law of motion
(c) first law of motion
(d) all of these laws

14. The direction of impulse is

(a) same as that of the net force
(b) opposite to that of the net force
(c) same as that of the final velocity
(d) same as that of the initial velocity

15. When a body is stationary

(a) the combination of forces acting on it balances each other
(b) the body is in vacuum
(c) the force acting on it is not in contact with it
(d) there is no force acting on it

16. When an elevator cabin falls down, the cabin and all the bodies fixed in the cabin are accelerated with respect to

(a) man standing on earth
(b) ceiling of elevator
(c) floor of elevator
(d) man standing in the cabin

17. If the applied force is doubled, then coefficient of friction is

(a) not changed
(b) tripled
(c) halved
(d) doubled

18. Which of the following statements about friction is true?

(a) Frictional force can accelerate a body
(b) Friction can be reduced to zero
(c) Frictional force is proportional to the area of contact between the two surfaces
(d) Sliding friction is always greater than rolling friction

19. What are the effects if force is acting on a moving body in a direction perpendicular to the direction of motion

(a) The direction of motion changes
(b) All of these
(c) The acceleration changes uniformly
(d) The speed changes uniformly

20. A cyclist taking turn bends inwards while a car passenger taking same turn is thrown outwards. The reason is

(a) car is heavier than cycle
(b) car has four wheels while cycle has only two
(c) Difference in the speed of the two
(d) cyclist has to counteract the centrifugal force while in the case of car only the passenger is thrown by this force

21. A cyclist bends while taking turn in order to

(a) provide required centripetal force
(b) reduce apparent weight
(c) reduce speed
(d) reduce friction

22. A car moving on a horizontal road may be thrown out of the road in taking a turn

(a) due to the lack of proper centripetal force
(b) due to the rolling frictional force between the tyre and road
(c) due to the reaction of the ground
(d) by the gravitational force

23. To avoid slipping while walking on ice, one should take smaller steps because:

(a) frictional force of ice is large
(b) of larger normal reaction
(c) frictional force of ice is small
(d) of smaller normal reaction

24. A particle is moving with a constant speed along a straight line path. A force is not required to:

(a) Increase its speed
(b) Decrease its momentum
(c) Change the direction
(d) Keep it moving with uniform speed

25. If the tension in the cable of 1000 kg elevator is 1000 kg weight, the elevator:

(a) is accelerating upwards
(b) is accelerating downwards
(c) may be at rest or accelerating
(d) may be at rest or in uniform motion

Answer 2

1. Answer: (d) the inertial mass

Explanation: Inertial mass is a mass parameter giving the inertial resistance to acceleration of the body when responding to all types of force.

2. Answer: (a) 4 N

Explanation: F = m \(\times\) a

= 2m/s² \(\times\)​ 2

= 4 N​​​​​​

3. Answer: (d) three

Explanation: Change in momentum for each bullet fired is

= \(\frac{40}{1000}\times1200\)

= 48N

If a bullet fired exerts a force of 48N on man’s hand so ρ man can exert maximum force of 144N, number of bullets that can be fired

=144/48

= 3 bullets

4. Answer: (a) by Newtons first law

Explanation: when a moving bus stop suddenly passenger thrown forward because inertia of motion ( Newton's first law of motion), lower part of body comes to rest but upper body tend to maintain uniform motion. hence passenger thrown forward.

5. Answer: (a) 10 kg m/s

Explanation: P = m \(\times \) v

P = 5 \(\times\) 2

P = 10 kg m/s

6. Answer: (d) strong force

Explanation: The strong nuclear force pulls together protons and neutrons in the nucleus. At very small distances only, such as those inside the nucleus, this strong force overcomes the electromagnetic force, and prevents the electrical repulsion of protons from blowing the nucleus apart.

7. Answer: (d) opposite to the direction of the applied force

Explanation: Friction always oppose the relative slipping between two bodies. So it oppose the motion of block so that block is at rest.

8. Answer: (d) opposite to the direction of the applied force

Explanation: When we try to slide a body on a surface, the motion of the body is opposed by a force called the force of friction. The frictional force arises due to intermolecular interaction. When an external force (F) is applied to move the body and the body does not move, then the frictional force acts opposite to applied force F and is equal to the applied force i.e., F−f = 0 frictional force,f  and  applied force F. When the body remains at rest, the frictional force is called the static friction. Static friction is a self-adjusting force.

9. Answer: (d) ranks fourth in strength

Explanation: Actually, gravity is the weakest of the four fundamental forces. Ordered from strongest to weakest, the forces are (1) the strong nuclear force, (2) the electromagnetic force, (3) the weak nuclear force, and 4) gravity. Because they both have mass, the two protons exert gravitational attraction on each other.

10. Answer: (d) both b and d 

Explanation: A reference frame attached to the earth is cannot be an inertial frame because the earth is revolving around the sun and rotating about its own axis.

11. Answer: (a) inertia

Explanation: Newton’s first law of motion defines the inertia of the body. It states that everybody has a tendency to remain in its state (either rest or motion) due to its inertia.

12. Answer: (b) Unable to change by itself the state of rest and or uniform linear motion

Explanation: Inertia is defined as  "A property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

13. Answer: (c) first law of motion

Explanation: Newton's first law of motion is related to physical independence of force, by definition "It states – Every body continues to be in a state of rest or uniform motion in a straight line, except in so far as it be compelled by an externally impressed force to act otherwise.

14. Answer: (a) same as that of the net force

Explanation: The impulse is the quantity defined as the force multiplied by the time it is applied. It is a vector quantity that has the same direction as the force.

15. Answer: (a) the combination of forces acting on it balances each other

Explanation: For the body to be stationary, net external force acting on it must be equal to zero which is possible only when the combination of forces acting on it balance each other.

Answer 3

16. Answer: (a) man standing on earth

Explanation: When an elevator cabin comes down, the cabin and all the bodies fixed in the cabin are accelerated with respect to the man standing on the earth. The elevator cabin is coming down and because of this, all the bodies will experience a downward force, hence the elevator cabin is a non-inertial frame.

17. Answer: (a) not changed

Explanation: The coefficient of friction is a property of the two surfaces in contact. If we double the normal force, we double the amount of friction, but the coefficient of friction is the same, since the nature of the two surfaces in contact has not changed.

18. Answer: (d) Sliding friction is always greater than rolling friction

Explanation: It is easy to roll the body in compare to sliding  so the sliding friction is always greater then rolling friction.

19. Answer: (a) The direction of motion changes

Explanation: As force is perpendicular to the direction of motion there will be no change in speed of the body but the direction of motion of the body will keep on changing continuously .

20. Answer: (d) cyclist has to counteract the centrifugal force while in the case of car only the passenger is thrown by this force

Explanation: A cyclist taking turn bends inwards while a car passenger taking same turn is thrown outwards. The reason is Cyclist has to counteract the centrifugal force while in the case of car only the passenger is thrown by this force.

21. Answer: (a) provide required centripetal force

Explanation: While bending the force of friction provides the necessary centripetal force but sometimes when the velocity is high, the centripetal force provided by friction is not enough and the cyclist has to bend. By doing so, the normal force acting on the cyclist also has a horizontal component which provides additional centripetal force.

22. Answer: (a) due to the lack of proper centripetal force

Explanation: When an object takes a turn two forces come to act.

1. centripetal force
2. centrifugal force

Centripetal force acts inward (towards the centre of the circular turn). This is provided by the frictional force. When the speed is large, required centripetal force to stay in the circular path increases. But friction is unable to provide large centripetal force and hence the body is thrown outwards.

23. Answer: (c) frictional force of ice is small

Explanation: To avoid slipping one should take smaller steps because the frictional force of ice is small. Smaller steps will give larger normal force and more the normal force more the friction.
Also the advantage of talking small steps is that lateral forces are decreased. When we put down are foot it will be pushing forwards on the concrete and at the end of the step it will be pushing backwards. Hence larger the step these forward and backward forces will be larger increasing the chances of slipping.

24. Answer: (d) Keep it moving with uniform speed

Explanation: Newton's first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force. This postulate is known as the law of inertia. Hence a force is not required to keep the particle moving with uniform speed.

25. Answer: (d) may be at rest or in uniform motion

Explanation: Since T=mg, it implies that the elevator may be at rest or in uniform motion.

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