1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

2D Friction-Finding the Force of Friction without Mu

  1. Sep 27, 2012 #1
    2D Friction--Finding the Force of Friction without Mu

    1. The problem statement, all variables and given/known data
    A 1500kg car is parked on a 4-degree incline. The acceleration of gravity is 9.8 m/s2. Find the force of friction keeping the car from sliding down the incline.


    2. Relevant equations
    FW=mg
    [Sigma]Fy=0, so Top=Bottom
    "Friction is Fun:" fs=musFN
    Since the degree of incline is 4 degrees, the angle with the "left" part of the x-axis on the free-body diagram and FW is 86 degrees.

    3. The attempt at a solution
    After drawing a free-body diagram, I calculated Fw=(1500)(9.8)=14700N
    Next, I used Top=Bottom to calculate FN=14700sin(86)=14664.19154N
    Third, fs=musFN. This is where I got stuck. How can I solve for the force of friction without mu?
     
  2. jcsd
  3. Sep 27, 2012 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Re: 2D Friction--Finding the Force of Friction without Mu

    In your free body diagram, you should have oriented your axis so the y points normal to the plane and x points along the plane.

    In the +y direction, you have a normal force N and a component of the weight force W.
    In the +x direction you have a friction force f and the other component of the weight force.

    In each direction, write out all the forces in a row (some of them will be negative), put "+" signs between them and an "= ma" at the end. What is the acceleration?
    Remember to write W just as W (you can put W=mg later if you need to) and friction just as f (you can put f=μsN later if you need to.)

    This will give you two equations, and you have two unknowns. The unknowns are f and N.
    But I think you'll find that the equation with f in it has no other unknowns so you can solve it right off.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook