Question 1

A student claims: "An object cannot be in mechanical equilibrium when only a single force is acting on it." Do you agree or disagree with this statement? Explain your reasoning.

Accepted Answer

Agree; mechanical equilibrium requires the net force $$\sum \vec{F} = 0$$, so if only one force acts, the net force cannot be zero.

Question 2

Jerry pulls horizontally to the right on a crate with a force of 200 N, and it slides to the right across a rough floor at a constant speed. Which force diagram best represents all the forces acting on the crate?

Accepted Answer

A rightward force of 200 N, a leftward friction force of 200 N, an upward normal force, and a downward gravitational force.

Question 3

A box is pushed across a floor at a steady speed. Which of the following statements is true about the forces acting on the box?

Accepted Answer

The applied force is equal to the friction force.

Question 4

Which of the following best describes static friction?

Accepted Answer

It acts when an object is not moving and prevents motion up to a maximum value.

Question 5

A hockey puck slides across ice with negligible friction. What is required to keep it moving at constant velocity?

Accepted Answer

No force is required; inertia keeps it moving.

Question 6

If the net force acting on an object doubles, what happens to its acceleration?

Accepted Answer

The acceleration doubles.

Question 7

Which of the following is true about the relationship between mass and inertia?

Accepted Answer

They are directly proportional.

Question 8

A 1-kg object weighs 10 N on Earth. What would its weight be on the Moon, where $$g = 1.6\ \mathrm{m/s^2$}$$?

Accepted Answer

$$1.6\ \mathrm{N}$$

Question 9

Which of the following statements about friction is correct?

Accepted Answer

Sliding friction is mostly independent of speed for solid surfaces.

Question 10

A 2-kg object is acted on by a net force of 8 N. What is its acceleration?

Accepted Answer

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

Question 11

Which of the following is the correct formula for calculating the weight of an object?

Accepted Answer

$$W = mg$$

Question 12

A 50-kg student stands on the surface of the Earth ($$M_{Earth} = 5.98 	imes 10$$^{24}$$\ \mathrm{kg}$$, $$R_{Earth} = 6.38 	imes 10^6$\ \mathrm{m}). $$Using the Law of Universal Gravitation, what is the gravitational force between the student and the Earth? ($$G = 6.67 	imes 10$$^{-11}$$\ \mathrm{N\cdot m^2$/kg^2$$}$)

Accepted Answer

$$F = 490\ \mathrm{N}$$

Question 13

If the distance between two objects is tripled, what happens to the gravitational force between them according to Newton's Law of Universal Gravitation?

Accepted Answer

It becomes one-ninth as large.

Question 14

A car is skidding on a road. If the friction force is 100 N at low speed, what is the friction force at a higher speed (assuming solid surfaces and no other changes)?

Accepted Answer

It is about 100 N.

Question 15

Which of the following best describes terminal velocity?

Accepted Answer

The speed at which the net force on a falling object is zero because air resistance equals gravity.

Question 16

A 7-kg rock weighs 11.4 N on the surface of the Moon. What is the acceleration due to gravity on the Moon?

Accepted Answer

$$g = 1.63\ \mathrm{m/s^2$}$$

Question 17

Which of the following is NOT a property of mass?

Accepted Answer

It changes with location.

Question 18

If the mass of an object is doubled while the net force remains the same, what happens to the acceleration?

Accepted Answer

It is halved.

Question 19

Which of the following is a correct statement of Newton's Second Law of Motion?

Accepted Answer

The net force on an object is equal to its mass times its acceleration: $$F = ma$$

Question 20

Which of the following best explains why trucks have many tires?

Accepted Answer

To spread the load and reduce tire wear.

Physics Study Guide: Forces, Equilibrium, and Newton's Laws

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