Q: A 20 kg box is pulled across a rough floor with a constant velocity. If the coefficient of kinetic friction is $$\mu_k = 0.4$$, what is the magnitude of the friction force?

$$f = 20 \times 9.8 \times 0.4 = 78.4 N$$

Q: A 5 kg box is at rest on a horizontal surface. If the coefficient of static friction is $$\mu_s = 0.5$$, what is the maximum static friction force that can act on the box?

$$f_{s,\text{max}} = 5 \times 9.8 \times 0.5 = 24.5 N$$

Question 1

A mass $$M is $$suspended as shown in the first image by two massless cables, one making an angle $$	heta$$ with the ceiling. If the system is in equilibrium, which equation correctly expresses the vertical force balance on the mass?

Accepted Answer

$$2T \cos 	heta = Mg$$

Question 2

Refer to the free-body diagrams in images 2–5. Which diagram best represents the forces acting on a box sliding to the right at constant speed on a rough horizontal surface?

Accepted Answer

Image 3

Question 3

The position vs. time graph in image 6 shows a straight line with positive slope. What does this indicate about the net force acting on the object?

Accepted Answer

The net force is zero.

Question 4

In the system shown in image 7, two wires each make a $$30^\circ$$ angle with the vertical and support a mass with weight $$w$$ and an additional downward force $$F. $$What is the correct expression for the tension $$T in $$each wire?

Accepted Answer

$$T = \frac{w + F}{2 \cos 30^\circ}$$

Question 5

In image 8, a person pushes on box G, which is in contact with box H. According to Newton's Third Law, what is the reaction force to the person's push on box G?

Accepted Answer

The push of box G against the person.

Question 6

A person pulls a crate with a rope at a $$30^\circ$$ angle above the horizontal, as shown in image 9. If the tension in the rope is $$T$$, what is the vertical component of the tension?

Accepted Answer

$$T \sin 30^\circ$$

Question 7

A person pushes a box up an inclined plane as shown in image 10. If the box moves at constant speed, which of the following statements is true?

Accepted Answer

The net force on the box is zero.

Question 8

A box is being pulled across grass (image 11) and does not move. If the pulling force is $$F$$, what is the magnitude of the static friction force acting on the box?

Accepted Answer

Equal to $$F$$

Question 9

A man pulls a box with a rope as shown in image 12. Which force is the Newton's Third Law pair to the tension force exerted by the rope on the box?

Accepted Answer

The tension force exerted by the box on the rope.

Question 10

A right triangle has sides of length 4 and 6, as shown in image 14. What is the length of the hypotenuse $$C$$?

Accepted Answer

$$C = \sqrt{52}$$

Question 11

In image 15, a person pushes a sled at $$30^\circ$$ above the horizontal in scenario (a) and pulls at $$30^\circ$$ above the horizontal in scenario (b). In which scenario is the normal force on the sled greater?

Accepted Answer

Scenario (a): pushing

Question 12

A crane supports a 400 N load as shown in image 16. If cable $$T_B$$ makes a $$40^\circ$$ angle with the vertical, what is the vertical component of the tension in cable $$T_B$$?

Accepted Answer

$$T_B \cos 40^\circ$$

Question 13

A box is pulled with a force $$F at an $$angle $$	heta$$ above the horizontal. If the box moves at constant velocity, what is the relationship between the horizontal component of $$F$$ and the friction force $$f$$?

Accepted Answer

$$F \cos 	heta = f$$

Question 14

A 20 kg box is pulled across a rough floor with a constant velocity. If the coefficient of kinetic friction is $$\mu_k = 0.4$$, what is the magnitude of the friction force?

Accepted Answer

$$f = 20 	imes 9.8 	imes 0.4 = 78.4 N$$

Question 15

A 5 kg box is at rest on a horizontal surface. If the coefficient of static friction is $$\mu_s = 0.5$$, what is the maximum static friction force that can act on the box?

Accepted Answer

$$f_{s,	ext{max}} = 5 	imes 9.8 	imes 0.5 = 24.5 N$$

EXAM 3 PRACTICE

Study Guide - Practice Questions

Study Guide - Flashcards