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Homework Help: Work and Friction Questions

  1. Nov 17, 2008 #1
    1. The problem statement, all variables and given/known data

    A worker pushes a 93N crate 10m up a 37 degree incline with constant velocity. The worker exerts a force of 85N parallel to the incline.

    a. How much work does he do?
    b. How much work is done by gravity?
    c. How much work is done by friction?
    d. What is the coefficient of friction between the box and the incline?

    2. Relevant equations

    Work = Force x Distance
    Ff = (u)(Fn)

    3. The attempt at a solution

    Part A:

    work = (85 N)(10 m) = 850 joules

    Part B:

    work = (10 * sin(37)) * 93 N = 560 N

    I believe these are correct. The parts that I do not know how to do are C and D. Anyone know how? I greatly appreciate all help :)
  2. jcsd
  3. Nov 17, 2008 #2


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    Homework Helper
    Gold Member


    The net work done by non conservative forces (i.e. the force of the push and friction) will equal the negative of the change in energy of the box:

    [tex]W_{non-conservative}=-\Delta E[/tex]

    Can you use this to find the answers for parts C and D?
  4. Nov 17, 2008 #3
    Thank you for your help!

    So the force of friction is -850 joules?

    For Part D, I am supposed to use the friction force for Ff and the normal force for Fn, right?

    Is the normal force 93 N?
    Last edited: Nov 17, 2008
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