Q: A 10 kg box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.4. What is the maximum force that can be applied horizontally before the box starts to move? (Take $$g = 10\ \mathrm{m/s^2$})$$

$$f_{s,\text{max}} = \mu_s N = 0.4 \times 10 \times 10 = 40\ \mathrm{N}$$

Q: A 4 kg block is acted on by three horizontal forces: 10 N to the right, 20 N to the left, and 15 N to the right. What is the net force?

$$F_{\text{net}} = 10 + 15 - 20 = 5\ \mathrm{N}$$\ to\ the\ right

Question 1

Which experiment, famously performed from the Leaning Tower of Pisa, demonstrated that objects of different masses fall at the same rate in the absence of air resistance?

Accepted Answer

Galileo's free-fall experiment

Question 2

According to Newton's First Law, what will happen to a hockey puck sliding on perfectly smooth ice if no forces act on it?

Accepted Answer

It will continue moving at a constant velocity.

Question 3

A 10 kg box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.4. What is the maximum force that can be applied horizontally before the box starts to move? (Take $$g = 10\ \mathrm{m/s^2$})$$

Accepted Answer

$$f_{s,	ext{max}} = \mu_s N = 0.4 	imes 10 	imes 10 = 40\ \mathrm{N}$$

Question 4

Which of the following best describes the normal force acting on a book resting on a table?

Accepted Answer

It acts perpendicular to the surface and supports the book's weight.

Question 5

A 5 kg object is acted on by a net force of 20 N to the right. What is its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{20}{5} = 4\ \mathrm{m/s^2$}$$

Question 6

A box is being pushed across a floor at constant speed. Which statement is true about the forces acting on the box?

Accepted Answer

The applied force is equal to the friction force.

Question 7

Which of the following is NOT an example of Newton's Third Law?

Accepted Answer

A book rests on a table due to gravity.

Question 8

A 4 kg block is acted on by three horizontal forces: 10 N to the right, 20 N to the left, and 15 N to the right. What is the net force?

Accepted Answer

$$F_{	ext{net}} = 10 + 15 - 20 = 5\ \mathrm{N}$$\ to\ the\ right

Question 9

A 4 kg block is acted on by a net horizontal force of 8 N. What is its acceleration?

Accepted Answer

$$a = \frac{8}{4} = 2\ \mathrm{m/s^2$}$$

Question 10

A ball hangs at rest from a string attached to the ceiling. What is the net force acting on the ball?

Accepted Answer

The net force is zero.

Question 11

Which of the following statements about friction is correct?

Accepted Answer

Static friction must be overcome for an object to start moving.

Question 12

A 50 kg astronaut weighs less on the Moon than on Earth. Which of the following is true?

Accepted Answer

The astronaut's weight is less on the Moon.

Question 13

If two equal-magnitude forces act on a box in opposite directions, what can be said about the box's motion?

Accepted Answer

The box could be moving at constant velocity.

Question 14

A 10 kg box is pulled with a force of 60 N to the right and a friction force of 20 N opposes the motion. What is the acceleration of the box?

Accepted Answer

$$a = \frac{60 - 20}{10} = 4\ \mathrm{m/s^2$}$$

Question 15

Which equation correctly relates weight, mass, and gravitational acceleration?

Accepted Answer

$$W = m g$$

Question 16

A person pushes a wall with a force of 100 N. According to Newton's Third Law, what is the force exerted by the wall on the person?

Accepted Answer

100 N in the opposite direction

Question 17

Which of the following best explains why the coefficient of static friction is usually greater than the coefficient of kinetic friction for the same surfaces?

Accepted Answer

Static friction involves both molecular bonds and surface roughness, while kinetic friction involves only surface roughness.

Question 18

A 12 kg box is at rest on a horizontal surface. The coefficient of kinetic friction is 0.3. If a horizontal force of 50 N is applied, what is the acceleration of the box? ($$g = 10\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = \frac{50 - (0.3 	imes 12 	imes 10)}{12} = \frac{50 - 36}{12} = \frac{14}{12} \approx 1.17\ \mathrm{m/s^2$}$$

Question 19

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

Accepted Answer

An object at rest remains at rest and an object in motion remains in motion at constant velocity unless acted on by an unbalanced force.

Newton's Laws of Motion and Forces: Foundations of Classical Mechanics

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