Q: Which of the following equations correctly represents Newton's third law in vector form?

$$\vec{F}_{A\ \text{on}\ B} = -\vec{F}_{B\ \text{on}\ A}$$

Question 1

Which of the following statements correctly describes Newton's third law of motion?

Accepted Answer

For every force, there is an equal and opposite force acting on a different object.

Question 2

A person standing on a skateboard throws a ball forward. What happens to the person and why?

Accepted Answer

The person moves backward due to the reaction force from throwing the ball.

Question 3

Consider a box resting on a table. Which of the following is the correct action-reaction pair according to Newton's third law?

Accepted Answer

The force of the table on the box and the force of the box on the table.

Question 4

A hammer strikes a nail. According to Newton's third law, what is the force pair involved?

Accepted Answer

The force of the hammer on the nail and the force of the nail on the hammer.

Question 5

A horse pulls a cart forward. The cart pulls back on the horse with an equal and opposite force. Why does the system move forward?

Accepted Answer

Because the horse exerts a force on the ground, which pushes the horse (and cart) forward.

Question 6

An astronaut in orbit around Earth feels weightless. Which statement is correct regarding the gravitational force between the astronaut and Earth?

Accepted Answer

The astronaut exerts a gravitational force on Earth equal in magnitude and opposite in direction to Earth's force on the astronaut.

Question 7

A person pushes against a wall but the wall does not move. What is the reaction force according to Newton's third law?

Accepted Answer

The force of the wall pushing back on the person.

Question 8

If the net force on an object is zero, which of the following must be true according to Newton's laws?

Accepted Answer

The object's velocity must be constant.

Question 9

A train is accelerating forward. If there is no friction, what force causes the train to accelerate?

Accepted Answer

The force of the ground on the train wheels.

Question 10

Which of the following equations correctly represents Newton's third law in vector form?

Accepted Answer

$$\vec{F}_{A\ 	ext{on}\ B} = -\vec{F}_{B\ 	ext{on}\ A}$$

Question 11

A stack of three books rests on a table. Which force increases as more books are added to the stack?

Accepted Answer

The normal force exerted by the table on the bottom book.

Question 12

A person jumps off the ground. Which force propels the person upward?

Accepted Answer

The force of the ground pushing up on the person.

Question 13

Which of the following is NOT an action-reaction pair according to Newton's third law?

Accepted Answer

The friction force between a box and the table and the normal force from the table on the box.

Question 14

A car of mass $$m is at $$rest on a flat road. What is the magnitude of the normal force exerted by the road on the car?

Accepted Answer

$$mg$$

Question 15

If a person pulls upward on their own hair while standing on the ground, can they lift themselves off the ground?

Accepted Answer

No, because all forces are internal and there is no net external force.

Question 16

A train consists of three cars connected by couplers. If the engine exerts a force $$F on $$the first car and each car has mass $$m$$, what is the acceleration $$a of $$the train (assuming no friction)?

Accepted Answer

$$a = \frac{F}{3m}$$

Question 17

Which of the following best explains why astronauts in orbit feel weightless?

Accepted Answer

Because they are in free fall, accelerating at the same rate as their spacecraft.

Question 18

Which of the following is the correct SI unit for force?

Accepted Answer

Newton (N)

Question 19

A skier pushes against the snow with their poles to move forward. Which force actually propels the skier?

Accepted Answer

The force of the snow on the skier.

Newton's Third Law: Concepts, Applications, and Free-Body Diagrams

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