# Physics Questions and Answers – Newton’s Third Law of Motion

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Newton’s Third Law of Motion”.

1. The forces involved in Newton’s third law act ____
a) On the same object
b) On different objects
c) In same direction
d) On five bodies

Explanation: The two forces involved in Newton’s third law are the cause force and the reaction force. The cause force acts on the contact surface or the contact body by the parent body. Whereas the reaction force acts on the parent body by the contact body.

2. Two bodies in contact experience forces in ________
a) Same direction
b) Opposite directions
c) Perpendicular directions
d) Five different directions

Explanation: The two bodies in contact will follow Newton’s third law of motion. The third law states that for every action there is an equal and opposite reaction. The two bodies will experience each other’s reaction forces in opposite directions.

3. A batsman hits a ball with a force a 5 N. What force does the bat experience?
a) 5 N
b) 10 N
c) 15 N
d) 20 N

Explanation: From Newton’s third law we know that for every for every action, there is an equal and opposite reaction. From this we can say that the bat experiences a force of 5 N.

4. A driver hits a light pole with a force a 100 N. What force does the car experience?
a) 100 N
b) 10 N
c) 150 N
d) 200 N

Explanation: From Newton’s third law we know that for every for every action, there is an equal and opposite reaction. From this we can say that the car experiences a force of 100 N by the light pole.

5. A truck with a mass of 2500 Kg travelling with an acceleration of 5 m/s2 hits a scooter. What force does the truck experience?
a) 12500 N
b) 500 N
c) 10000 N
d) 2500 N

Explanation: From Newton’ second law we get force on scooter = 2500 x 5 = 12500 N. From Newton’s third law we know that for every for every action, there is an equal and opposite reaction. From this we can say that the truck experiences a force of 5 N.

6. A man and a kid accidentally hit each other. What is true about the forces experienced by them?
a) They are equal in magnitude
b) They are different in magnitude
c) They are same in direction
d) They are at an angle of 1.57 rad

Explanation: From the third law of motion, we know that the cause force and the reaction forces are equal in magnitude and opposite in direction. Hence, from this knowledge, we can say that the man and the kid will experience forces in opposite directions and in equal magnitude.

7. A man is standing still. The force by the man on the earth is $$\vec{F1}$$. The force by the earth on the man is $$\vec{F2}$$. Which one of the following is true?
a) $$\vec{F1} = \vec{F2}$$
b) $$\vec{F1} = -\vec{F2}$$
c) $$\vec{F1} = 5(\vec{F2})$$
d) $$2(\vec{F1}) = \vec{F2}$$

Explanation: According to the third law of motion, every action has an equal and opposite reaction. Hence every action force is equal in magnitude to its reaction but in opposite direction. Hence $$\vec{F1} = -\vec{F2}$$ is the correct answer. 