Q: A block is pulled by two forces, $F_1$ and $F_2$, at angles $\theta_1$ and $\theta_2$ above the horizontal, respectively. What is the $y$-component of the net force?

$F_1 \sin \theta_1 + F_2 \sin \theta_2$

Question 1

Which of the following statements best describes Newton's First Law of Motion?

Accepted Answer

An object at rest tends to stay at rest, and an object in motion tends to stay in uniform motion unless acted upon by a net force.

Question 2

A box of mass $m$ is sliding down a rough incline plane at angle $	heta$ with respect to the horizontal. If the coefficient of kinetic friction is $\mu_k$, what is the magnitude of the frictional force acting on the box?

Accepted Answer

$\mu_k m g \cos 	heta$

Question 3

Which of the following is NOT a property of a force?

Accepted Answer

A force acts only on objects at rest.

Question 4

A car of mass $1200\ \mathrm{kg}$ accelerates from rest under a net force of $3600\ \mathrm{N}$. What is the acceleration of the car?

Accepted Answer

$3.0\ \mathrm{m/s^2}$

Question 5

Which of the following best describes the normal force acting on an object at rest on a horizontal surface?

Accepted Answer

It is equal in magnitude and opposite in direction to the gravitational force.

Question 6

A block is pulled by two forces, $F_1$ and $F_2$, at angles $	heta_1$ and $	heta_2$ above the horizontal, respectively. What is the $y$-component of the net force?

Accepted Answer

$F_1 \sin 	heta_1 + F_2 \sin 	heta_2$

Question 7

Which of the following is the correct vector sum notation for the net force acting on an object?

Accepted Answer

$\sum \vec{F} = \vec{F}_1 + \vec{F}_2 + \vec{F}_3 + \ldots$

Question 8

A person pulls a sled of mass $m$ with a force $F$ at an angle $	heta$ above the horizontal. What is the horizontal component of the pulling force?

Accepted Answer

$F \cos 	heta$

Question 9

Which of the following is true about tension in a massless rope connecting two objects?

Accepted Answer

The tension is the same throughout the rope.

Question 10

A block of mass $m$ is sliding on a horizontal surface with friction. If a constant force $F$ is applied and the coefficient of kinetic friction is $\mu_k$, what is the acceleration of the block?

Accepted Answer

$\dfrac{F - \mu_k m g}{m}$

Question 11

Which of the following is a correct statement of Newton's Third Law?

Accepted Answer

For every action, there is an equal and opposite reaction acting on different objects.

Question 12

A ball is suspended by two strings, one above and one below. If the lower string is jerked quickly, which string will break first and why?

Accepted Answer

The lower string, because the force is concentrated due to inertia.

Question 13

A car of mass $m$ is moving in a circle of radius $r$ at constant speed $v$. What is the direction of the net force acting on the car?

Accepted Answer

Radially inward toward the center.

Question 14

Which of the following is the correct formula for the magnitude of the centripetal force acting on an object of mass $m$ moving at speed $v$ in a circle of radius $r$?

Accepted Answer

$F_c = \dfrac{m v^2}{r}$

Question 15

A free-body diagram is useful for solving problems involving multiple forces because:

Accepted Answer

It helps visualize all the forces acting on an object and their directions.

Question 16

A block of mass $m$ is pulled up a frictionless incline at angle $	heta$ by a force $F$ parallel to the incline. What is the acceleration of the block?

Accepted Answer

$a = \dfrac{F - m g \sin 	heta}{m}$

Question 17

Which of the following is the SI unit of force?

Accepted Answer

Newton ($\mathrm{N}$)

Question 18

A car of mass $m$ is moving at speed $v$ and comes to a stop due to a constant friction force $F_f$. What is the stopping distance $d$?

Accepted Answer

$d = \dfrac{m v^2}{2 F_f}$

Question 19

Which of the following is true about the net force acting on an object in equilibrium?

Accepted Answer

The net force is zero.

Newton's Laws of Motion: Forces and Free-Body Diagrams

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