Newton's Third Law Motion Important Questions

---

Very Short Answers Questions [1 Mark Questions]

Ques. A man and a kid accidentally hit each other. What is true about the forces experienced by them?

1. They are the same in direction
2. They are equal in magnitude
3. They are different in magnitude
4. They are at an angle of 1.57 rad

Ans. The correct answer is b. They are equal in magnitude

Explanation: According to the third law of motion, the cause and reaction forces are equal in magnitude and opposing in direction. Therefore the man and the kid will be subjected to forces in opposing directions and of equal magnitude.

Ques. The forces involved in Newton’s Third Law act

1. In the same direction
2. On the same object
3. On five bodies
4. On different objects

Ans. The correct answer is d. On different objects

Explanation: Newton's third law includes two forces: the action force and the reaction force. The parent body exerts an action force on the contact surface or contact body. The contact body, on the other hand, exerts a reaction force on the parent body.

Ques. A batsman hits a ball with a force of 5 N. What force does the bat experience?

1. 5 N
2. 15 N
3. 20 N
4. 25 N

Ans. The correct answer is a. 5 N

Explanation: Newton's third law states that for every action, there is an equal and opposite reaction. Therefore the bat will also experience a force of 5 N.

Ques. Two bodies in contact experience forces in

1. Opposite directions
2. Five different directions
3. Perpendicular directions
4. Same direction

Ans. The correct answer is a. Opposite directions

Explanation: Newton's third law of motion will be followed by the two bodies in contact. According to the third law, every action has an equal and opposite reaction. The reaction forces of the two bodies will be experienced in opposite directions.

Ques. How many laws of motion were put forth by Newton?

1. 1
2. 2
3. 3
4. 4

Ans. The correct answer is c. 3

Explanation: There are three laws of motion given by Newton, known as Newton’s laws of motion.

Ques. Gravitational force is a

1. Non-contact force
2. Contact force
3. Semi contact force
4. Neither contact nor non-contact force

Ans. The correct answer is a. Non-contact force

Explanation: Gravitational force is a non-contact force.

Ques. Newton’s first law of motion is known as

1. The law of mass
2. The law of inertia
3. The law of velocity
4. The law of momentum

Ans. The correct answer is b. The law of inertia

Explanation: According to Newton’s first law of motion, a body cannot change its state of rest or motion until and unless an external force is applied to it. Hence it is known as the law of inertia.

Ques. Which is the contact force?

1. Frictional force
2. Gravitational force
3. Electric force
4. Magnetic force

Ans. The correct answer is a. Frictional force

Explanation: Contact force is defined as the force applied on a body due to another body in contact with it. Hence frictional force is a contact force.

Ques. What is the force acting between the Sun and the Earth?

1. Magnetic force
2. Electromagnetic force
3. Gravitational force
4. Electric force

Ans. The correct answer is c. Gravitational force

Explanation: The rotation of the Earth around the Sun is due to the gravitational force between them.

Ques. Rock climbers pull their vertical rope ______ to move up.

1. Downwards
2. Upwards
3. Sideway
4. None of the above

Ans. The correct answer is a. Downwards

Explanation: Rock climbers applied an action force by pulling the rope vertically downward. Hence the rope exerts a reaction force in the upward direction, that helps the climber to move up.

---

Short Answers Questions [2 Marks Questions]

Ques. What is Newton’s third law of motion?

Ans. Newton's third law of motion states that whenever one body exerts a force on another, the first body experiences a force of the same magnitude as the force applied but in the opposite direction.

Ques. What is an action-reaction pair?

Ans. When a force is exerted by body A on another body B, there is also a force exerted by body B on body A. These forces are equal in magnitude and act in opposite directions. Such a pair of forces is known as an action-reaction pair. Any of these two forces may be called the “action”, and the other will be the “reaction”.

Ques. What is the formula of Newton’s third law of motion?

Ans. Let 

• F_AB is the force exerted on body A due to body B.
• F_BA is the force exerted on body B due to body A.

Then, the formula of Newton’s third law of motion is given by

F_AB = – F_BA

Ques. A man pushes a wall with a force of 100 N towards the north. What force does the wall exert on the man?

Ans. According to Newton’s third law of motion,

Action force = - Reaction force

The force on the wall due to man is considered as action force. Hence the force exerted on the man due to the wall in the opposite direction will be considered as reaction force.

Therefore, the force exerted by the wall on the man = 100 N towards the south.

Ques. What is force?

Ans. Force is defined as an external cause experienced by a body as a result of interacting with another body. When two objects interact, a force is applied to each of them. 

Ques. What is the law of conservation of momentum?

Ans. Conservation of momentum is a physics general law that states that the quantity known as momentum, which describes motion, never changes in an isolated collection of objects; that is, the total momentum of a system remains constant.

Ques. What is the relationship between Newton's third law of motion and conservation of momentum?

Ans. According to Newton's third law, the forces on the two objects are equal in magnitude and opposite in direction. In the absence of any external force, one object gains momentum and the other loses momentum, conserving the total momentum of the system.

Ques. How does Newton's third law apply to rockets?

Ans. The launch of a rocket is based on Newton's Third Law of Motion. Thrust is produced by a rocket engine through action and reaction. The engine creates hot exhaust gasses, which exit the engine through the back end. In the opposite reaction, a pushing force is produced.

Ques. What is Newton’s second law of motion?

Ans. According to Newton’s third law of motion, the rate of change of momentum of a body is directly proportional to the applied force and it takes place in the direction in which the force acts.

Read More:

---

Long Answers Questions [3 Marks Questions]

Ques. What are the examples of action and reaction force?

Ans. The following are examples of the action and reaction forces

Ques. Two bodies A and B of masses m and 2m are moving towards each other. The only force in the system is a mutually attractive force between A and B. At an instant, the acceleration of the body A is a. What is the acceleration of B at this instant?

Ans. Let 

• F_AB is the force of attraction experienced by body A due to body B.
• F_BA is the force of attraction experienced by body B due to body A.

Given

• The acceleration body A, a_A = a
• The mass of body A, m_A = m
• The mass of body B, m_B = 2m

According to Newton’s third law of motion,

F_AB = – F_BA

⇒ m_Aa_A = – m_Ba_B

On substituting the values, we get

m x a = - (2m)a_B

⇒ a_B = - (a/2)

Ques. What are the applications of Newton’s third law of motion?

Ans. The following are the applications of Newton’s third law of motion

• Recoiling of a gun: When a bullet is fired from a gun, it exerts a forward force on the bullet and the bullet exerts an equal and opposite force on the gun. Due to the large mass of the gun, it moves a small distance backward and gives a backward jerk to the shoulder of the gunman.

• Walking of a man on the ground: When we walk on the ground, our foot pushes the ground backward and in return, the ground pushes our foot forward.

---

Very Long Answers Questions [5 Marks Questions]

Ques. What are the examples of Newton’s third law motion?

Ans. The following are examples of Newton’s third law of motion

• The movement of a fish through water is an example of Newton's third law of motion. The fins of a fish are used to push water backward. This push pushes the fish forward. The magnitude of the force on the water equals the magnitude of the force on the fish in the opposite direction.
• The flight of the bird is an example of Newton's third law motion. The wings of the bird push the air downward. The air pushes the bird upward.
• A swimmer pushes up against the water, and the water pushes him back.
• Lift is produced by helicopters by pushing the air downward, resulting in an upward reaction force.
• Climbers push the rope vertically downward to climb up.
• A person walking on the ground exerts a force on the ground with his feet in the backward direction (action force), and the ground exerts an opposite and equal force in the forward direction as a reaction force, so we can walk on the ground or on the floor.

Ques. What are the limitations of Newton’s third law of motion?

Ans. The following are the limitations of Newton’s third law of motion

• Newton's Third Law is quite effective for macroscopic objects interacting at low speeds, but it may fail at the quantum scale or at relativistic speeds.
• When a force is distributed across a large area, such as gravity, identifying an equal and opposite reaction force can be difficult.
• External equal and opposite reaction forces do not exist for forces within an object, such as electrostatic attraction between atoms.
• The frictional force that prevents objects in contact from moving is not strictly equal to the force applied. It is determined by factors such as surface roughness.
• The normal force that keeps one object from entering another during contact is not an action-reaction pair with gravity. It is caused by atomic-level electromagnetic repulsion.
• Some kinetic energy is lost when objects collide inelastically due to heat, sound, and so forth. As a result, the post-collision velocities may not exactly obey Newton's Third Law.

Ques. What is the significance of Newton’s third law of motion?

Ans. When we used to write equations for calculating net force on a system, we sometimes came across situations where it was difficult to tell which forces were external and which were internal. The significance of Newton's third law of motion becomes essential in this case. It can help in recognizing the external forces affecting the system. 

The significance of Newton's third law can be understood by performing an easy analysis of human movement. 

• Take swimming as an example. When we applied force to the walls of the swimming pool, the wall applied the same magnitude of force to our feet, causing us to accelerate in the other direction because the pool's applied force was opposite to us. 
• Because these forces of similar magnitude but opposing in direction act on separate systems, they cannot cancel each other out.
• In order to move in one direction, a force must be exerted in the opposite direction. 
• Similar principles are used when walking, playing baseball, driving a car, rocket propulsion, helicopter lift, and so forth. 
• All of these processes use Newton's third law in some way.

For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates

---

Check-Out: