Physics: Newton's Third Law Worksheet

Question 1

State Newton's Third Law in your own words. Include what is meant by an action-reaction force pair.

Accepted Answer

Newton's Third Law says that when one object exerts a force on a second object, the second object exerts an equal-magnitude force in the opposite direction on the first object. An action-reaction force pair always acts on two different objects.

Question 2

A student pushes on a wall with a force of 80 N to the east. What force does the wall exert on the student?

Accepted Answer

The wall exerts a force of 80 N to the west on the student. The forces are equal in magnitude and opposite in direction.

Question 3

A rocket engine pushes hot gases downward. Explain how Newton's Third Law helps the rocket move upward.

Accepted Answer

The rocket pushes the gases downward, and the gases push the rocket upward with an equal and opposite force. This upward force is the thrust that accelerates the rocket.

Question 4

A 0.20 kg tennis ball hits a racket. During contact, the racket exerts a 120 N force on the ball. What force does the ball exert on the racket?

Accepted Answer

The ball exerts a 120 N force on the racket in the opposite direction. Newton's Third Law says the forces in the interaction are equal in magnitude and opposite in direction.

Question 5

Two ice skaters push off from each other. Skater A has a mass of 50 kg, and Skater B has a mass of 75 kg. During the push, which skater experiences the larger force? Explain.

Accepted Answer

Both skaters experience forces of equal magnitude. Skater A may have a larger acceleration because the same force acts on a smaller mass, but the interaction forces are equal.

Question 6

In the same ice skater situation, why does the 50 kg skater accelerate more than the 75 kg skater if the forces are equal?

Accepted Answer

The 50 kg skater accelerates more because acceleration is force divided by mass. With the same force, the smaller mass has the greater acceleration.

Question 7

A book rests on a table. Identify the Newton's Third Law partner force for the force of the table pushing upward on the book.

Accepted Answer

The partner force is the book pushing downward on the table. These two forces act on different objects and are equal in magnitude and opposite in direction.

Question 8

A book rests on a table. A student says, 'The upward normal force and the downward weight of the book are a Newton's Third Law pair.' Explain why this statement is incorrect.

Accepted Answer

The statement is incorrect because both the normal force and the weight act on the same object, the book. A Newton's Third Law pair must act on two different objects.

Question 9

When you walk forward, your foot pushes backward on the ground. What force helps you move forward?

Accepted Answer

The ground pushes forward on your foot through static friction. This forward friction force helps accelerate your body forward.

Question 10

A swimmer pushes water backward with her hands. Use Newton's Third Law to explain how she moves forward.

Accepted Answer

The swimmer pushes the water backward, and the water pushes the swimmer forward with an equal and opposite force. That forward force moves the swimmer through the water.

Question 11

A car tire pushes backward on the road as the car accelerates forward. Identify the reaction force and explain its role.

Accepted Answer

The reaction force is the road pushing forward on the tire. This forward static friction force provides the external force that accelerates the car forward.

Question 12

A 60 kg astronaut in space pushes a 10 kg tool with a force of 18 N to the right. What force does the tool exert on the astronaut, and in what direction?

Accepted Answer

The tool exerts an 18 N force on the astronaut to the left. The forces are equal in magnitude and opposite in direction.

Question 13

For the astronaut and tool in the previous problem, calculate the acceleration of the astronaut caused by the tool's force.

Accepted Answer

The astronaut's acceleration is 0.30 m/s² to the left because a = F divided by m = 18 N divided by 60 kg = 0.30 m/s².

Question 14

A bug hits the windshield of a moving truck. Compare the force of the bug on the truck with the force of the truck on the bug.

Accepted Answer

The bug and the truck exert equal-magnitude forces on each other in opposite directions. The bug has a much larger acceleration because its mass is much smaller.

Question 15

A student fires a ball from a spring launcher. The launcher pushes the ball forward with a force of 35 N. Identify the action-reaction pair and describe why the launcher recoils.

Accepted Answer

The launcher pushes the ball forward with 35 N, and the ball pushes the launcher backward with 35 N. The launcher recoils because the backward force from the ball accelerates the launcher in the opposite direction.

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Physics: Newton's Third Law

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