Question 1

A hammer strikes a nail, driving it into a piece of wood. According to Newton's Third Law, which of the following statements is correct?

Accepted Answer

The force the hammer exerts on the nail is equal in magnitude and opposite in direction to the force the nail exerts on the hammer.

Question 2

A 2 kg ball is dropped from rest and falls toward the Earth. According to Newton's Third Law, what is the force that the ball exerts on the Earth?

Accepted Answer

Equal in magnitude and opposite in direction to the gravitational force the Earth exerts on the ball.

Question 3

When you sit on a chair, your weight pushes down on the chair. What is the reaction force according to Newton's Third Law?

Accepted Answer

The chair pushes up on you with a force equal in magnitude to your weight.

Question 4

A person pushes a crate across a rough surface. Which of the following is an example of an action/reaction pair in this scenario?

Accepted Answer

The force the person exerts on the crate and the force the crate exerts back on the person.

Question 5

Two ice skaters, Skater A (50 kg) and Skater B (70 kg), push off against each other on frictionless ice. If Skater A moves away with a velocity of $$2\ \mathrm{m/s}$$, what is the velocity of Skater B immediately after the push?

Accepted Answer

$$1.43\ \mathrm{m/s} in $$the opposite direction to Skater A

Question 6

A car accelerates forward because the tires push backward on the road. What is the reaction force according to Newton's Third Law?

Accepted Answer

The road pushes forward on the tires with an equal and opposite force.

Question 7

A 5 kg box is pulled to the right by a rope with a force of $$20\ \mathrm{N} on a $$frictionless surface. What is the acceleration of the box?

Accepted Answer

$$4\ \mathrm{m/s^2$}$$

Question 8

Two boxes, A (2 kg) and B (3 kg), are connected by a massless string and pulled to the right with a force of $$25\ \mathrm{N}. If $$the surface is frictionless, what is the tension in the string between the boxes?

Accepted Answer

$$15\ \mathrm{N}$$

Question 9

A 200 kg crate is placed in the back of a 1000 kg truck. The coefficient of static friction between the crate and the truck bed is $$\mu_s = 0.40. $$What is the maximum force the truck can exert on the crate without it sliding?

Accepted Answer

$$784\ \mathrm{N}$$

Question 10

A block of mass $$m is $$suspended from a rope. If the block is at rest, what is the tension $$T in $$the rope?

Accepted Answer

$$T = mg$$

Question 11

Two blocks, A (4 kg) and B (6 kg), are connected by a light string over a frictionless pulley. Block A is on a table, and Block B hangs off the edge. If the system is released from rest, what is the acceleration of the system? (Assume $$g = 10\ \mathrm{m/s^2$}$$ and ignore friction.)

Accepted Answer

$$2\ \mathrm{m/s^2$}$$

Question 12

A person is walking forward on a sidewalk. What is the direction of the friction force acting on the person's foot during the step?

Accepted Answer

Forward, in the direction the person is walking.

Question 13

A rocket launches vertically upward. Which force is responsible for the rocket's upward acceleration?

Accepted Answer

The thrust force from the rocket engines pushing down on the exhaust gases, which in turn push up on the rocket.

Question 14

In a system of two boxes connected by a massless string, Box A (2 kg) and Box B (3 kg), pulled by a force $$F on $$Box B, which of the following is true about the tension in the string?

Accepted Answer

The tension is less than the force $$F$$ and transmits the force from Box B to Box A.

Question 15

A 1000 kg safe is lowered 3.0 m to the ground using a rope over a frictionless, massless pulley. If the safe is lowered at constant speed, what is the tension in the rope?

Accepted Answer

$$9800\ \mathrm{N}$$

Question 16

Which of the following best describes an interaction diagram in the context of Newton's laws?

Accepted Answer

A diagram that represents all objects in a system and the interactions (forces) between them.

Question 17

If two objects interact via a force, which of the following is always true according to Newton's Third Law?

Accepted Answer

The forces are equal in magnitude, opposite in direction, and act on different objects.

Newton’s Third Law and Interacting Objects

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