Q: A 5-kg box is pulled to the right with a force of 20 N while friction exerts a force of 8 N to the left. What is the acceleration of the box?

$$a = \frac{F_{\text{net}}}{m} = \frac{20\ \mathrm{N} - 8\ \mathrm{N}}{5\ \mathrm{kg}} = 2.4\ \mathrm{m/s^2$}$$

Q: A 50-kg person weighs less on the Moon than on Earth. If $$g_{\text{Earth}} = 9.8\ \mathrm{m/s^2$}$$ and $$g_{\text{Moon}} = 1.6\ \mathrm{m/s^2$}$$, what is the person's weight on the Moon?

$$W = m \cdot g = 50\ \mathrm{kg} \times 1.6\ \mathrm{m/s^2$} = 80\ \mathrm{N}$$

Question 1

A 50-kg astronaut is floating in space far from any planets or stars. If she pushes a 10-kg tool away from her with a force of 20 N, what is her acceleration immediately after the push?

Accepted Answer

$$a = \frac{F}{m} = \frac{20\ \mathrm{N}}{50\ \mathrm{kg}} = 0.4\ \mathrm{m/s^2$}$$

Question 2

A car suddenly stops after hitting a wall, and the passenger without a seatbelt continues moving forward. Which law of motion best explains why the passenger keeps moving?

Accepted Answer

Newton's First Law (Law of Inertia)

Question 3

A helicopter hovers in place. According to Newton's Third Law, what is the reaction force to the blades pushing air downward?

Accepted Answer

The air pushes the blades upward with an equal and opposite force.

Question 4

A 5-kg box is pulled to the right with a force of 20 N while friction exerts a force of 8 N to the left. What is the acceleration of the box?

Accepted Answer

$$a = \frac{F_{	ext{net}}}{m} = \frac{20\ \mathrm{N} - 8\ \mathrm{N}}{5\ \mathrm{kg}} = 2.4\ \mathrm{m/s^2$}$$

Question 5

Which of the following statements about mass and weight is correct?

Accepted Answer

Weight depends on the gravitational field, but mass does not.

Question 6

A rocket moves in space by expelling exhaust gases backward. Which law of motion explains the rocket's forward movement?

Accepted Answer

Newton's Third Law: For every action, there is an equal and opposite reaction.

Question 7

Two blocks (2 kg and 4 kg) are tied together and pulled to the right with a force of 30 N. Frictional forces of 6 N and 8 N act to the left on the 2 kg and 4 kg blocks, respectively. What is the net acceleration of the system?

Accepted Answer

$$a = \frac{30\ \mathrm{N} - 6\ \mathrm{N} - 8\ \mathrm{N}}{2\ \mathrm{kg} + 4\ \mathrm{kg}} = \frac{16\ \mathrm{N}}{6\ \mathrm{kg}} = 2.67\ \mathrm{m/s^2$}$$

Question 8

A 50-kg person weighs less on the Moon than on Earth. If $$g_{	ext{Earth}} = 9.8\ \mathrm{m/s^2$}$$ and $$g_{	ext{Moon}} = 1.6\ \mathrm{m/s^2$}$$, what is the person's weight on the Moon?

Accepted Answer

$$W = m \cdot g = 50\ \mathrm{kg} 	imes 1.6\ \mathrm{m/s^2$} = 80\ \mathrm{N}$$

Question 9

Which of the following best describes inertia?

Accepted Answer

The tendency of an object to resist changes in its state of motion.

Question 10

A 10-kg box is at rest on a frictionless surface. Two forces, $$F_1 = 15$$\ \mathrm{N}$$ to the right and F_2$ = 10\ \mathrm{N} to $$the left, act on it. What is the acceleration of the box?

Accepted Answer

$$a = \frac{15\ \mathrm{N} - 10\ \mathrm{N}}{10\ \mathrm{kg}} = 0.5\ \mathrm{m/s^2$}$$\ 	ext{to the right}

Question 11

Which of the following is NOT a contact force?

Accepted Answer

Gravitational force

Question 12

A 1-kg object and a 10-kg object are dropped from the same height in a vacuum. Which statement is true?

Accepted Answer

Both objects experience the same acceleration.

Question 13

A person pushes a box across the floor at constant velocity. Which statement is true about the forces acting on the box?

Accepted Answer

The applied force is equal in magnitude and opposite in direction to the frictional force.

Question 14

A 2-kg block is pulled with a net force of 10 N. What is its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{10\ \mathrm{N}}{2\ \mathrm{kg}} = 5\ \mathrm{m/s^2$}$$

Question 15

Which of the following scenarios best illustrates Newton's Third Law?

Accepted Answer

A swimmer pushes water backward and moves forward.

Question 16

A 10-kg box is acted on by two perpendicular forces: $$F_1 = 6$$\ \mathrm{N}$$ upward and F_2$ = 8\ \mathrm{N} to $$the right. What is the magnitude of the box's acceleration?

Accepted Answer

$$a = \frac{\sqrt{6^2$ + 8^2$}}{10} = \frac{10}{10} = 1\ \mathrm{m/s^2$}$$

Question 17

A patient’s leg is suspended by a traction system. If the mass of the leg is 8 kg, what is the weight of the leg?

Accepted Answer

$$W = m \cdot g = 8\ \mathrm{kg} 	imes 9.8\ \mathrm{m/s^2$} = 78.4\ \mathrm{N}$$

Question 18

Which of the following is a field force?

Accepted Answer

Gravitational force

Newton’s Laws of Motion: Forces and Dynamics

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