Q: A person pulls a $20.0\ \mathrm{kg}$ box with a rope at an angle of $30.0^\circ$ above the horizontal with a force of $40.0\ \mathrm{N}$. What is the vertical component of the pulling force?

$F_{y} = 40.0\ \mathrm{N} \times \sin 30.0^\circ = 20.0\ \mathrm{N}$

Q: A $5.0\ \mathrm{kg}$ block is at rest on a $30^\circ$ incline. The coefficient of static friction is $0.5$. What is the minimum value of $\mu_s$ required to prevent the block from sliding?

$\mu_s = \tan 30^\circ = 0.577$

Q: A $10.0\ \mathrm{kg}$ box is pulled with a force of $50.0\ \mathrm{N}$ at an angle of $30.0^\circ$ above the horizontal. If the coefficient of kinetic friction is $0.20$, what is the net force in the horizontal direction?

$F_{net} = 50.0\cos 30.0^\circ - 0.20 \times (98.0 - 50.0\sin 30.0^\circ)$

Question 1

A 20.0-kg box rests on a table. What is the weight of the box?

Accepted Answer

$196\ \mathrm{N}$

Question 2

A 10.0-kg box is placed on top of a 20.0-kg box, both at rest on a table. What is the normal force the table exerts on the 20.0-kg box?

Accepted Answer

$294\ \mathrm{N}$

Question 3

With the 10.0-kg box on the 20.0-kg box, what is the normal force that the 20.0-kg box exerts on the 10.0-kg box?

Accepted Answer

$98.0\ \mathrm{N}$

Question 4

If the stack of boxes is turned upside down so that the 10.0-kg box is on the bottom and the 20.0-kg box is on top, what happens to the normal force between the boxes?

Accepted Answer

The normal force between the boxes would be the same

Question 5

A 14.0-kg lawn mower is pushed at constant speed with a force of $F = 88.0\ \mathrm{N}$ at an angle of $45.0^\circ$ to the horizontal. What is the horizontal component of the applied force?

Accepted Answer

$62.2\ \mathrm{N}$

Question 6

A 14.0-kg lawn mower is pushed at constant speed with a force of $F = 88.0\ \mathrm{N}$ at $45.0^\circ$ to the horizontal. What is the normal force exerted vertically upward on the mower by the ground?

Accepted Answer

$199\ \mathrm{N}$

Question 7

A crate is placed on the bed of a truck. The coefficient of static friction between the crate and the truck is $\mu_s = 0.75$. What is the maximum acceleration the truck can have without the crate sliding?

Accepted Answer

$a_{max} = \mu_s g = 7.35\ \mathrm{m/s^2}$

Question 8

A 3.2-kg paint bucket is hanging by a massless cord from another 3.2-kg paint bucket, also hanging by a massless cord. If the buckets are at rest, what is the tension in the upper cord?

Accepted Answer

$62.7\ \mathrm{N}$

Question 9

A block of mass $m$ slides down a frictionless incline of angle $	heta$. What is the acceleration of the block down the ramp?

Accepted Answer

$a = g \sin 	heta$

Question 10

A $10.0\ \mathrm{kg}$ box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is $0.40$. What is the minimum horizontal force required to start moving the box?

Accepted Answer

$39.2\ \mathrm{N}$

Question 11

A $5.0\ \mathrm{kg}$ block is sliding down a rough incline of $30^\circ$ with a coefficient of kinetic friction $\mu_k = 0.20$. What is the net acceleration of the block?

Accepted Answer

$a = g(\sin 30^\circ - 0.20 \cos 30^\circ)$

Question 12

Which of the following best describes the normal force acting on an object on an incline of angle $	heta$?

Accepted Answer

$F_N = mg \cos 	heta$

Question 13

A person pulls a $20.0\ \mathrm{kg}$ box with a rope at an angle of $30.0^\circ$ above the horizontal with a force of $40.0\ \mathrm{N}$. What is the vertical component of the pulling force?

Accepted Answer

$F_{y} = 40.0\ \mathrm{N} 	imes \sin 30.0^\circ = 20.0\ \mathrm{N}$

Question 14

A $10.0\ \mathrm{kg}$ box is at rest on a horizontal surface. If a horizontal force of $30.0\ \mathrm{N}$ is applied and the coefficient of kinetic friction is $0.25$, what is the acceleration of the box?

Accepted Answer

$a = \frac{30.0\ \mathrm{N} - (0.25)(98.0\ \mathrm{N})}{10.0\ \mathrm{kg}} = 0.5\ \mathrm{m/s^2}$

Question 15

Which of the following statements about friction is correct?

Accepted Answer

The maximum static friction force is $F_{s, max} = \mu_s F_N$

Question 16

A $100\ \mathrm{kg}$ box is placed on top of a $20.0\ \mathrm{kg}$ box, both at rest on a table. What is the normal force the table exerts on the $20.0\ \mathrm{kg}$ box?

Accepted Answer

$1176\ \mathrm{N}$

Question 17

A block of mass $m$ is at rest on a rough incline. Which force counteracts the component of gravity perpendicular to the incline?

Accepted Answer

The normal force

Question 18

A $5.0\ \mathrm{kg}$ block is at rest on a $30^\circ$ incline. The coefficient of static friction is $0.5$. What is the minimum value of $\mu_s$ required to prevent the block from sliding?

Accepted Answer

$\mu_s = 	an 30^\circ = 0.577$

Question 19

A $10.0\ \mathrm{kg}$ box is pulled with a force of $50.0\ \mathrm{N}$ at an angle of $30.0^\circ$ above the horizontal. If the coefficient of kinetic friction is $0.20$, what is the net force in the horizontal direction?

Accepted Answer

$F_{net} = 50.0\cos 30.0^\circ - 0.20 	imes (98.0 - 50.0\sin 30.0^\circ)$

Forces, Normal Force, and Friction: Study Notes for Giancoli Chapter 4

Study Guide - Practice Questions

Study Guide - Flashcards