Call Now to Set Up Tutoring:

(888) 888-0446

AP Physics C: Mechanics : Forces

Study concepts, example questions & explanations for AP Physics C: Mechanics

Create An Account

All AP Physics C: Mechanics Resources

2 Diagnostic Tests 92 Practice Tests Question of the Day Flashcards Learn by Concept

Example Questions

Example Question #1 : Forces

Weightlessness is experienced when the normal force equals __________.

Possible Answers:

zero

the mass of the object

the force due to gravity

a negative value

Correct answer:

zero

Explanation:

"Weightlessness" is analogous to free-fall (neglecting air resistance), during which the only force on an object is the force of gravity. When normal force becomes zero, the object loses physical contact with the surface.

When normal force is equal to the force of gravity, the object is in equilibrium and the net vertical force is zero. This results in zero acceleration, but does not result in "weightlessness." Mass is not a force, and negative force values merely indicate relative direction (assuming correct calculations)

Report an Error

Example Question #2 : Forces

A book of mass 1kg is held to a vertical wall by a person's hand applying a 20N force directly toward the wall. The wall has a static friction coefficient of 0.3 and a kinetic friction coefficient of 0.2. With the book held at rest, what the is frictional force keeping the book from sliding down the wall?

Possible Answers:

58.8N

39.2N

Correct answer:

Explanation:

Frictional force is calculated using the normal force and the friction coefficient. Since the book is at rest (not in motion), we use the coefficient of static friction.

$F_f=\mu_sF_N$

The normal force will be equal and opposite the force pushing directly into the surface; in this case, that means the normal force will be 20N.

Solve for the force of friction:

F_f=(0.3)(20N)=6N

Report an Error

Example Question #1 : Friction And Normal Force

$\begin{align*}&\text{A block of mass }190kg\text{ rests on an incline of }33^{\circ}\\&\text{It is also partially supported by a rope with a tension of }559.17N\\&\text{What is the normal force acting on the block from the surface?}\\&g=9.81\frac{m}{s^2}\end{align*}$

Possible Answers:

1015.15N

1094.24N

1563.2N

710.61N

Correct answer:

1094.24N

Explanation:

Normalwrope

$\begin{align*}&\text{To solve a problem of force balance, a good idea is to draw}\\&\text{it out. Since the block is at rest, i.e. stationary, the sum}\\&\text{of forces acting on it must be equal to zero. The forces acting}\\&\text{on it are gravity (in the form of the mass times the gravitational}\\&\text{constant), the force of the rope supporting it, a normal force,}\\&\text{and since it’s on an incline, a frictional force to balance}\\&\text{it all out. Notice that the tension in the rope mitigates some}\\&\text{of the gravitational force (as illustrated in the upper left}\\&\text{corner) to lessen what is applied to the slope:}\\&F_{mass}=m*g\\&F_{normal}=(F_{mass}-F_{rope})*cos(a)\\&F_{friction}=(F_{mass}-F_{rope})*sin(a)\\&F_{normal}=(190kg(9.81\frac{m}{s^2})-559.17N)(cos(33^{\circ}))\\&F_{normal}=1094.24N\end{align*}$

Report an Error

Example Question #1 : Forces

$\begin{align*}&\text{A block of mass }233kg\text{ rests on an incline of }81^{\circ}\\&\text{What is the normal force acting on the block from the surface?}\\&g=9.81\frac{m}{s^2}\end{align*}$

Possible Answers:

230.13N

357.57N

2285.73N

2257.59N

Correct answer:

357.57N

Explanation:

Normal

Report an Error

Example Question #1 : Friction And Normal Force

$\begin{align*}&\text{A block of mass }187kg\text{ rests on an incline of }83^{\circ}\\&\text{What is the normal force acting on the block from the surface?}\\&g=9.81\frac{m}{s^2}\end{align*}$

Possible Answers:

223.57N

1820.8N

185.61N

1834.47N

Correct answer:

223.57N

Explanation:

Normal

Report an Error

Example Question #1 : Normal Force

$\begin{align*}&\text{A block of mass }267kg\text{ rests on an incline of }49^{\circ}\\&\text{What is the normal force acting on the block from the surface?}\\&g=9.81\frac{m}{s^2}\end{align*}$

Possible Answers:

201.51N

1976.79N

1718.4N

2619.27N

Correct answer:

1718.4N

Explanation:

Normal

Report an Error

Example Question #1 : Friction And Normal Force

$\begin{align*}&\text{A block of mass }112kg\text{ rests on an incline of }18^{\circ}\\&\text{It is also partially supported by a rope.}\\&\text{The normal force acting on the block is }417.98N\\&\text{What is the tension felt in the rope?}\\&g=9.81\frac{m}{s^2}\end{align*}$

Possible Answers:

339.52N

1044.94N

659.23N

1098.72N

Correct answer:

659.23N

Explanation:

Normalwrope

$\begin{align*}&\text{To solve a problem of force balance, a good idea is to draw}\\&\text{it out. Since the block is at rest, i.e. stationary, the sum}\\&\text{of forces acting on it must be equal to zero. The forces acting}\\&\text{on it are gravity (in the form of the mass times the gravitational}\\&\text{constant), the force of the rope supporting it, a normal force,}\\&\text{and since it’s on an incline, a frictional force to balance}\\&\text{it all out. Notice that the tension in the rope mitigates some}\\&\text{of the gravitational force (as illustrated in the upper left}\\&\text{corner) to lessen what is applied to the slope:}\\&F_{mass}=m*g\\&F_{normal}=(F_{mass}-F_{rope})*cos(a)\\&F_{rope}=F_{mass}-\frac{F_{normal}}{cos(a)}\\&F_{rope}=1098.72N-\frac{417.98N}{cos(18^{\circ})}\\&F_{rope}=659.23N\end{align*}$

Report an Error

Example Question #3 : Friction And Normal Force

A $\small 3500kg$ truck traveling at $\smlal 25\frac{m}{s}$ suddenly brakes and skids to a halt. If the coefficient of kinetic friction between the tires and the road is $\small 0.4$ , how far does the truck skid before stopping?

Possible Answers:

24m

52m

80m

Correct answer:

80m

Explanation:

Relevant equations:

$\Delta K = W$

$K = \frac{1}{2}mv^2$

W = F*d

$F_f = \mu F_N$

Determine the truck's change in kinetic energy. Note that the final kinetic energy will be zero because it has no final velocity.

$K_i = \frac{1}{2}(3500kg)(25\frac{m}{s})^2=1,093,750J$

K_f=0

$\Delta K = K_f - K_i = -1,093,750 J$

Using the work-energy theorem, set change in kinetic energy equal to the work done by friction.

$\Delta K = -F_f d$

Substitute the equation for force of friction.

$\Delta K=-\mu F_Nd$

$\Delta K = -\mu (mg)d$

Use the given values for coefficient of friction, mass, and acceleration of gravity to solve for the distance.

$-1,093,750 J= -(0.4)(3500kg)(9.8\frac{m}{s^2})d$

$d = 79.7m \approx 80m$

Report an Error

Example Question #3 : Forces

A force of 40N is applied on a 14kg box to move it to the right. If the coefficient of friction between the box and the floor is 0.2, what is the acceleration of the box?

Possible Answers:

$0.2\frac{m}{s^2}$

$0\frac{m}{s^2}$

$2.0\frac{m}{s^2}$

$0.9\frac{m}{s^2}$

$3.4\frac{m}{s^2}$

Correct answer:

$0.9\frac{m}{s^2}$

Explanation:

The two horizontal forces acting on the box are the applied force of 40N to the right, and the friction force ( $\mu_kF_N$ )to the left. So the net horizontal force is written as the equation below.

$40N-\mu_kF_N=ma$

F_N=mg is the normal force. Solving for acceleration, a, we get the equation below.

$a=\frac{40N-\mu_kF_N}{m}$

We know the following from the question.

m=14kg

$g=9.8\frac{m}{s^2}$

$\mu_k=0.2$

$F_N=mg=(14kg)(9.8\frac{m}{s^2})=137.2N$

Thus, the acceleration is

$a=\frac{40N-(0.2)(137.2N)}{14kg}$

$a=0.9\frac{m}{s^2}$

Report an Error

Example Question #2 : Forces

A $\small 15kg$ crate is pulled across a horizontal floor at a constant velocity of $\small 3\frac{m}{s}$ . The coefficient of kinetic friction between the crate and the floor is $\small 0.20$ . If the rope pulling the crate is angled at $\small 45^o$ above the horizontal, what force must be applied to maintain this constant velocity?

Possible Answers:

35N

48N

83N

62N

52N

Correct answer:

35N

Explanation:

Relevant equations:

$F_{net}= ma$

$F_f=\mu F_N$

F_g = mg

Write net force equations for horizontal and vertical directions:

Horizontal: $F_{net, x} = F_{pull, x}-F_f$

Vertical: $F_{net,y}=F_N+F_{pull,y}-F_g$

Since the crate is not accelerating, $\small a=0\frac{m}{s^2}$ in each direction, implying that $\small F_{net,x}=F_{net,y}=0N$ .

Horizontal: $0 = F_{pull,x}-F_{f}$

Vertical: $0 = F_N + F_{pull,y}-F_g$

Express the horizontal and vertical components of the pulling force in terms of the total pulling force, $F_{pull}$ .

Horizontal: $0 = (F_{pull}*cos(45^o))-F_f$

Vertical: $0 = F_N + (F_{pull}*sin(45^o))-F_g$

Replace force of friction with its expression in terms of the normal force.

Horizontal: $0 = (F_{pull}*cos(45^o))-(\mu F_N)$

Rearrange to isolate the normal force.

Horizontal: $F_N =\frac{F_{pull}*cos(45^o)}{\mu}$

Substitute this term for the normal force in the net vertical force equation.

Vertical: $0 = (\frac{F_{pull}*cos(45^o)}{\mu})+(F_{pull}*sin(45^o))-F_g$

Solve to isolate the pulling force.

$F_{pull}=\frac{F_g*\mu}{cos(45^o)+\mu*sin(45^o)}$

Use the given values for the mass of the box, coefficient of friction, and acceleration of gravity to solve for the pulling force.

$F_{pull}=\frac{(15kg)(9.8 \frac{m}{s^2})(0.20)}{cos(45^o)+0.20*sin(45^o)}$

$F_{pull}=\frac{29.4N}{0.849}=34.65N\approx35N$

Report an Error

View Tutors

Blossom
Certified Tutor

University of Maryland-Baltimore County, Bachelor of Science, Computer Science.

View Tutors

Abhisek
Certified Tutor

University of Florida, Bachelor of Engineering, Computer Science.

View Tutors

Alyce
Certified Tutor

The University of Alabama, Master of Arts, German.

All AP Physics C: Mechanics Resources

2 Diagnostic Tests 92 Practice Tests Question of the Day Flashcards Learn by Concept

Popular Subjects

Reading Tutors in Miami, Computer Science Tutors in Seattle, Algebra Tutors in Chicago, Statistics Tutors in Phoenix, Chemistry Tutors in Miami, MCAT Tutors in Phoenix, Reading Tutors in Atlanta, Reading Tutors in Houston, GMAT Tutors in Denver, LSAT Tutors in Philadelphia

Popular Courses & Classes

GMAT Courses & Classes in Chicago, GRE Courses & Classes in San Francisco-Bay Area, ACT Courses & Classes in Washington DC, LSAT Courses & Classes in Washington DC, SAT Courses & Classes in Philadelphia, Spanish Courses & Classes in San Diego, SSAT Courses & Classes in Dallas Fort Worth, SSAT Courses & Classes in Seattle, LSAT Courses & Classes in Miami, SAT Courses & Classes in Boston

Popular Test Prep

GMAT Test Prep in Denver, ISEE Test Prep in Denver, SAT Test Prep in San Diego, ISEE Test Prep in Houston, ISEE Test Prep in Phoenix, SSAT Test Prep in Washington DC, GMAT Test Prep in Chicago, GRE Test Prep in Seattle, LSAT Test Prep in Houston, MCAT Test Prep in San Diego

DMCA Complaint

If you believe that content available by means of the Website (as defined in our Terms of Service) infringes one or more of your copyrights, please notify us by providing a written notice (“Infringement Notice”) containing the information described below to the designated agent listed below. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.

Your Infringement Notice may be forwarded to the party that made the content available or to third parties such as ChillingEffects.org.

Please be advised that you will be liable for damages (including costs and attorneys’ fees) if you materially misrepresent that a product or activity is infringing your copyrights. Thus, if you are not sure content located on or linked-to by the Website infringes your copyright, you should consider first contacting an attorney.

Please follow these steps to file a notice:

You must include the following:

A physical or electronic signature of the copyright owner or a person authorized to act on their behalf; An identification of the copyright claimed to have been infringed; A description of the nature and exact location of the content that you claim to infringe your copyright, in \ sufficient detail to permit Varsity Tutors to find and positively identify that content; for example we require a link to the specific question (not just the name of the question) that contains the content and a description of which specific portion of the question – an image, a link, the text, etc – your complaint refers to; Your name, address, telephone number and email address; and A statement by you: (a) that you believe in good faith that the use of the content that you claim to infringe your copyright is not authorized by law, or by the copyright owner or such owner’s agent; (b) that all of the information contained in your Infringement Notice is accurate, and (c) under penalty of perjury, that you are either the copyright owner or a person authorized to act on their behalf.

Send your complaint to our designated agent at:

Charles Cohn Varsity Tutors LLC
101 S. Hanley Rd, Suite 300
St. Louis, MO 63105

Or fill out the form below:

Do not fill in this field

Contact Information

* Full legal name

Company name

* Phone number

* Email address

Address

* Address1

Address2

* City

* State

* Zipcode

* Country

Complaint Details

* URL of copyrighted work (where your original material is located)

* Please describe the copyrighted work so that it may be easily identified

I am the owner, or an agent authorized to act on behalf of the owner of an exclusive right that is allegedly infringed.

I have a good faith belief that the use of the material in the manner complained of is not authorized by the copyright owner, its agent, or the law.

This notification is accurate.

I acknowledge that there may be adverse legal consequences for making false or bad faith allegations of copyright infringement by using this process.

* Signature (your digital signature is legally binding)

HIGH SCHOOL

GRADUATE SCHOOL

K-8

Search 50+ Tests

math tutoring

science tutoring

foreign languages

elementary tutoring

other

Search 350+ Subjects

AP Physics C: Mechanics : Forces

Study concepts, example questions & explanations for AP Physics C: Mechanics

All AP Physics C: Mechanics Resources

Example Questions

Example Question #1 : Forces

Example Question #2 : Forces

Example Question #1 : Friction And Normal Force

Example Question #1 : Forces

Example Question #1 : Friction And Normal Force

Example Question #1 : Normal Force

Example Question #1 : Friction And Normal Force

Example Question #3 : Friction And Normal Force

Example Question #3 : Forces

Example Question #2 : Forces

All AP Physics C: Mechanics Resources

Report an issue with this question

DMCA Complaint

Contact Information

Address

Complaint Details

Email address:
Your name:
Feedback: