Free Practice Quiz Question List

8 Friction and Mechanical Applications Online Quiz Questions

Use this free practice quiz with 20 questions to review 8 Friction and Mechanical Applications, test your knowledge, and prepare for your next test or exam.

20 questions

True or false

1 point

A block is at rest on a rough surface, and its contact with the surface is not at impending slip. Is its static friction force necessarily equal to $\mu_sN$ ?

A
True
B
False

Choose one

1 point

A body slides across a rough horizontal surface. Which statement describes the friction force in the simplified Coulomb model?

A
It adjusts from zero up to $\mu_sN$ .
B
It is modeled as $F_k=\mu_kN$ .
C
It is always equal to $\mu_sN$ .
D
It acts perpendicular to the contacting surfaces.

Choose all

1 point

Which statements about dry friction are correct? Select all that apply.

A
Friction can point in the same direction as a body's overall motion.
B
Friction always points opposite the body's overall motion.
C
The coefficients of friction are dimensionless.
D
Static friction must equal its limiting value whenever a body is at rest.

Fill in the blank

1 point

At impending slip, the magnitude of static friction is $F_s=$ .

Choose one

1 point

A $10\,\text{kg}$ block rests on a level floor. A horizontal force of $30\,\text{N}$ is applied, and $\mu_s=0.40$ . With no other vertical forces, what is the block's actual friction force?

A
$0\,\text{N}$ , because the block is at rest
B
Approximately $39.2\,\text{N}$ , because static friction is always maximal
C
$30\,\text{N}$ , opposite the applied force
D
More than $39.2\,\text{N}$ , because the block has mass

Fill in the blank

1 point

For two bodies in contact, the forces they exert on each other are . Show each force on its body's free-body diagram.

Choose one

1 point

A block rests on a plane inclined at angle $\theta$ above the horizontal. There are no other forces with components perpendicular to the plane. Which expression gives the normal force?

A
$N=mg\sin\theta$
B
$N=mg\cos\theta$
C
$N=mg\tan\theta$
D
$N=mg$

Written response

1 point

A block is about to slip downslope on a $30^\circ$ incline. There are no other forces besides gravity and the contact forces, and the block is at impending slip. What is the coefficient of static friction, rounded to three decimal places?

Choose all

1 point

When analyzing a wedge contacting multiple bodies, which procedures are appropriate? Select all that apply.

A
Draw a separate free-body diagram for the wedge and each body it contacts.
B
Assume friction points in the same direction at every wedge interface.
C
Determine the relative tendency to slip at each contact.
D
Use the limiting static-friction relation only where slip is impending.

True or false

1 point

Static friction on a driven wheel can point in the same direction as the wheel's motion.

A
True
B
False

Written response

1 point

In what unit must the wrap angle $\beta$ be expressed when using the limiting capstan relation?

Choose one

1 point

A flexible belt is about to slip on a rough pulley with $\mu_s=0.30$ and wrap angle $\beta=\pi$ radians. What is the limiting ratio $T_{\text{tight}}/T_{\text{slack}}$ , to two decimal places?

A
Approximately $0.30$
B
Approximately $2.57$
C
Exactly $\pi$
D
Approximately $3.14$

Open ended

1 point

Describe a systematic way to determine friction directions and apply the friction model when a wedge contacts multiple bodies. Explain how your approach changes if a contact is sliding rather than at impending slip.

Choose one

1 point

In an equilibrium calculation, you assume a direction for static friction and obtain a negative value for its signed magnitude. What does this result mean?

A
The body cannot be in equilibrium.
B
The actual friction direction is opposite the assumed direction.
C
The coefficient of friction must be negative.
D
The normal force must be zero.

True or false

1 point

If an additional applied force has a component perpendicular to an inclined plane, the normal force may differ from $mg\cos\theta$ , changing the maximum available static friction.

A
True
B
False

Written response

1 point

A friction coefficient describes a pair of surfaces and is not expressed using any measurement unit. What is the unit status of this coefficient?

Choose one

1 point

Which set of conditions must be satisfied by a rigid body in planar static equilibrium?

A
$\sum F_x=0$ , $\sum F_y=0$ , and $\sum M_O=0$
B
$\sum F_x=0$ and $\sum M_O=0$ , but not necessarily $\sum F_y=0$
C
$\sum F_y=0$ and $\sum M_O=0$ , but not necessarily $\sum F_x=0$
D
Zero net force is sufficient; the net moment may be nonzero

Choose one

1 point

A block is sliding across a horizontal surface. If the normal force is $80\,\text{N}$ and the kinetic-friction coefficient is $0.25$ , what is the friction force magnitude in the Coulomb model?

A
$0\,\text{N}$
B
$20\,\text{N}$
C
$32\,\text{N}$
D
$80\,\text{N}$

Choose one

1 point

A $10\,\text{kg}$ block rests on a level floor and is pushed horizontally with a $30\,\text{N}$ force. The coefficient of static friction is $0.40$ , and there are no other vertical forces. Using $g=9.81\,\text{m/s}^2$ , what is the actual static-friction force on the block?

A
$39.2\,\text{N}$ , equal to the maximum static friction
B
$30\,\text{N}$ , opposite the applied force
C
$9.8\,\text{N}$ , equal to the block's weight divided by ten
D
$0\,\text{N}$ , because the block remains at rest

Written response

1 point

A $12\,\text{kg}$ block rests on a plane inclined at $60^\circ$ above the horizontal. No other force has a component perpendicular to the plane. Using $g=9.81\,\text{m/s}^2$ , calculate the normal force. Enter your value in newtons to the nearest $0.01\,\text{N}$ ; answers within $0.01\,\text{N}$ are accepted.