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!

Work Done with Friction

  1. Feb 28, 2012 #1
    1. The problem statement, all variables and given/known data

    What is the minimum work needed to push a 900 kg car 880 m up along a 9.5° incline? Assume the effective coefficient of friction retarding the car is 0.20.


    2. Relevant equations
    W = F * d * cos (θ)
    Normal Force - mg * cos (9.5°)
    Force of kinetic friction = μ * Normal Force

    3. The attempt at a solution
    I drew out a free body diagram. The first thing I did:

    Normal Force - y component of gravity = 0 because it is not accelerating in the y direction.
    Normal Force - mg * cos (9.5°).
    Normal Force = mg * cos (9.5°).
    Normal Force = (900 kg)(9.8 m/s^2) * cos (9.5°)
    Normal Force = 1.73*10^3 N

    Second: Force of Kinetic Friction = (0.20)(8.69*10^3 N)
    Force of Kinetic Friction = 1.73*10 ^3N

    Work done by Friction : (1.73*10^3)(880 m) * sin 9.5°
    W = 2.5*10^5 J

    2.5*10^5 J + 1.28 *10^6 J (This is the minimum work required without friction. The first part of the question asked this and it confirmed this was the correct answer) =

    1.53 * 10^6 J
     
    Last edited: Feb 28, 2012
  2. jcsd
  3. Feb 28, 2012 #2

    Delphi51

    User Avatar
    Homework Helper

    I get 1.74 x 10^3 rather than your 1.73 for the friction force; don't know if that is important.

    In finding the work, why multiply by sin (9.5) ? The force of friction and the distance are in the same direction so no sine factor should be used.

    The rest of your calc looks good!
     
  4. Feb 28, 2012 #3
    Oops! I forgot - friction acts over the entire distance, not just the height as I was thinking.
     
  5. Feb 28, 2012 #4

    Delphi51

    User Avatar
    Homework Helper

    You bet.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Work Done with Friction
  1. Work Done by Friction (Replies: 11)

Loading...