Question 1

Which of the following best describes Newton's Third Law of Motion?

Accepted Answer

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Question 2

A person pushes against a wall with a force of $50\ \mathrm{N}$. According to Newton's Third Law, what is the magnitude and direction of the force the wall exerts on the person?

Accepted Answer

$50\ \mathrm{N}$, in the opposite direction

Question 3

When a bird flies by flapping its wings, which statement best explains how it is able to move upward?

Accepted Answer

The bird pushes air down, and the air pushes the bird up.

Question 4

A rocket launches by expelling gas downward. What is the reaction force that propels the rocket upward?

Accepted Answer

The gas pushes the rocket upward.

Question 5

In a tug-of-war, which team is more likely to win?

Accepted Answer

The team that pushes harder against the ground.

Question 6

A high-speed bus collides head-on with a bug. According to Newton's Third Law, which statement is true about the forces during the collision?

Accepted Answer

Both the bus and the bug experience forces of equal magnitude but opposite direction.

Question 7

When you step off a curb, Earth pulls you downward. What is the reaction force?

Accepted Answer

You pulling Earth upward.

Question 8

Why do you not sense Earth moving upward toward you when you step off a curb?

Accepted Answer

Earth moves, but by an imperceptible amount due to its large mass.

Question 9

A helicopter hovers in midair. What can be said about the forces acting on it?

Accepted Answer

Lift equals the force due to gravity.

Question 10

If the lift generated by a helicopter is greater than its weight, what will happen?

Accepted Answer

The helicopter will move upward.

Question 11

Two planets, A and B, exert gravitational forces on each other. If planet A is much more massive than planet B, how do their accelerations compare?

Accepted Answer

Planet B has a much greater acceleration than planet A.

Question 12

Which of the following statements about action and reaction forces is correct?

Accepted Answer

Action and reaction forces always act on different objects.

Question 13

A man pulls on a spring with a force $F$. What is the reaction force?

Accepted Answer

The spring pulls back on the man with a force $F$.

Question 14

If a book rests on a table, the table exerts an upward normal force equal in magnitude to the book's weight. Are these forces a Newton's Third Law pair?

Accepted Answer

No, because they act on the same object.

Question 15

A fish swims by pushing water backward with its fins. What is the reaction force?

Accepted Answer

The water pushes the fish forward.

Question 16

Which equation best represents Newton's Second Law of Motion?

Accepted Answer

$F = m a$

Question 17

If two ice skaters push off against each other, what determines which skater accelerates more?

Accepted Answer

The skater with less mass accelerates more.

Question 18

Which of the following is NOT a requirement for a Newton's Third Law force pair?

Accepted Answer

Both forces must act on the same object.

Question 19

A person jumps off a boat onto a dock. What happens to the boat?

Accepted Answer

The boat moves backward due to the reaction force.

Question 20

Which of the following is a real-world example of Newton's Third Law?

Accepted Answer

A swimmer pushes water backward and moves forward.

Newton's Third Law of Motion: Forces and Interactions

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