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 static friction force that can act on the box?

$$f_{s,\text{max}} = \mu_s F_N = 0.4 \times 10 \times 9.8 = 39.2\ \text{N}$$

Q: A 2 kg ball is dropped from rest and falls freely near the Earth's surface. Ignoring air resistance, what is the net force acting on the ball?

$$F_{\text{net}} = 2 \times 9.8 = 19.6\ \text{N}$$\ downward

Q: A 1000 kg car is moving at a constant velocity on a highway. The drag force acting on the car is given by $$F_{\text{drag}} = \frac{1}{2} C \rho A v^2$. If C = 0.3$, $$\rho = 1.3\ \text{kg/m}^3$$, A = 2.2$$\ \text{m}^2$$, and v = 30$$\ \text{m/s}$$, what is the magnitude of the drag force?

$$F_{\text{drag}} = \frac{1}{2} \times 0.3 \times 1.3 \times 2.2 \times 30^2$ = 386.1\ \text{N}$$

Q: A 50 kg box is pushed across a horizontal floor with a force of 200 N. The coefficient of kinetic friction between the box and the floor is 0.2. What is the acceleration of the box?

$$a = \frac{F_{\text{applied}} - f_k}{m} = \frac{200 - (0.2 \times 50 \times 9.8)}{50} = 1.04\ \text{m/s}^2$$

Q: A 100 N traffic light is suspended by two cables, each making a 37° angle with the horizontal. What is the tension in each cable?

$$T = \frac{100}{2 \sin 37^\circ} \approx 83\ \text{N}$$

Q: A 5 kg object is acted on by two forces: $$F_1 = 10$$\ \text{N}$$ to the right and F_2$ = 5\ \text{N} to $$the left. What is the acceleration of the object?

$$a = \frac{F_{\text{net}}}{m} = \frac{10 - 5}{5} = 1\ \text{m/s}^2$$\ to the right

Q: A 5 kg object is pulled by two forces of 4.6 N each, making a 40° angle between them. What third force will bring the object into equilibrium?

$$F_3 = 7.0$$\ \text{N}$$ to the right

Question 1

A car tire is rolling on a flat road without slipping. Which type of friction is primarily responsible for the force opposing the motion of the tire?

Accepted Answer

Rolling friction

Question 2

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 static friction force that can act on the box?

Accepted Answer

$$f_{s,	ext{max}} = \mu_s F_N = 0.4 	imes 10 	imes 9.8 = 39.2\ 	ext{N}$$

Question 3

A 2 kg ball is dropped from rest and falls freely near the Earth's surface. Ignoring air resistance, what is the net force acting on the ball?

Accepted Answer

$$F_{	ext{net}} = 2 	imes 9.8 = 19.6\ 	ext{N}$$\ downward

Question 4

A block is being pulled up a rough incline at a constant speed. Which statement is true about the forces acting on the block?

Accepted Answer

The net force on the block is zero.

Question 5

A 1000 kg car is moving at a constant velocity on a highway. The drag force acting on the car is given by $$F_{	ext{drag}} = \frac{1}{2} C ho A v^2$. If C = 0.3$, $$ho = 1.3\ 	ext{kg/m}^3$$, A = 2.2$$\ 	ext{m}^2$$, and v = 30$$\ 	ext{m/s}$$, what is the magnitude of the drag force?

Accepted Answer

$$F_{	ext{drag}} = \frac{1}{2} 	imes 0.3 	imes 1.3 	imes 2.2 	imes 30^2$ = 386.1\ 	ext{N}$$

Question 6

A 50 kg box is pushed across a horizontal floor with a force of 200 N. The coefficient of kinetic friction between the box and the floor is 0.2. What is the acceleration of the box?

Accepted Answer

$$a = \frac{F_{	ext{applied}} - f_k}{m} = \frac{200 - (0.2 	imes 50 	imes 9.8)}{50} = 1.04\ 	ext{m/s}^2$$

Question 7

A 70 kg astronaut is orbiting Earth in the International Space Station. What is the astronaut's weight while in orbit?

Accepted Answer

Zero, because the astronaut is in free fall and experiences weightlessness.

Question 8

A 100 N traffic light is suspended by two cables, each making a 37° angle with the horizontal. What is the tension in each cable?

Accepted Answer

$$T = \frac{100}{2 \sin 37^\circ} \approx 83\ 	ext{N}$$

Question 9

A 5 kg object is acted on by two forces: $$F_1 = 10$$\ 	ext{N}$$ to the right and F_2$ = 5\ 	ext{N} to $$the left. What is the acceleration of the object?

Accepted Answer

$$a = \frac{F_{	ext{net}}}{m} = \frac{10 - 5}{5} = 1\ 	ext{m/s}^2$$\ to the right

Question 10

A 250 kg crate is pushed up a 30° incline with a horizontal force of 5000 N. The coefficient of kinetic friction is 0.22. What is the acceleration of the crate?

Accepted Answer

$$a = 3.4\ 	ext{m/s}^2$$

Question 11

A ball is shot through a horizontal tube and emerges onto a flat table. Which path does the ball follow after it leaves the tube (neglecting air resistance)?

Accepted Answer

A straight line tangent to the tube's exit, then a parabolic path downward due to gravity.

Question 12

A 5 kg object is pulled by two forces of 4.6 N each, making a 40° angle between them. What third force will bring the object into equilibrium?

Accepted Answer

$$F_3 = 7.0$$\ 	ext{N}$$ to the right

Question 13

A skier is being towed up a hill at constant speed. Which forces act on the skier?

Accepted Answer

Gravity, normal force, friction, and tension from the tow rope.

Question 14

A 50 kg box rests on a horizontal surface. The coefficient of static friction is 0.3 and kinetic friction is 0.2. What is the friction force if a 140 N horizontal push is applied?

Accepted Answer

$$f_s = 140\ 	ext{N}$$

Question 15

A man stands on a scale in an elevator accelerating upward at $$2\ 	ext{m/s}^2. If $$his mass is 80 kg, what does the scale read?

Accepted Answer

$$w = mg + ma = 80 	imes 9.8 + 80 	imes 2 = 784 + 160 = 944\ 	ext{N}$$

Question 16

A 1 kg object falls through air and eventually reaches terminal speed. What is true at terminal speed?

Accepted Answer

The drag force equals the gravitational force: $$F_{	ext{drag}} = mg$$

Question 17

Which of the following best describes 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 a net force.

Force and Motion: Fundamental Concepts and Applications

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