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Mass pushed by horizontal force at constant speed on an incline

  1. Dec 5, 2007 #1
    3. A 52.3-kg trunk is pushed 5.95m at constant speed up a 28.0 degree incline by a constant horizontal force. The coefficient of kinetic friction between the trunk and the incline is .19 . Calculate the work done by a) the applied force and b) the force of gravity.

    Fy = N - mgcos28 = 0

    Fx = Fcos28 - f - mgsin28 = 0
    Fx = Fcos28 - ukN - mgsin28 = 0
    Fx = Fcos28 - ukmgsin28 - mgsin28 = 0
    F = 282.74N

    W = F*d
    W = 282.74N * 5.95m = 1682.3 J

    where am I going wrong?

    thanks
     
  2. jcsd
  3. Dec 5, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The applied force will have a y-component also.
     
  4. Dec 5, 2007 #3
    Fy = N - Fsin28 - mgcos28 = 0
    N = Fsin28 + mgcos28

    Fx = Fcos28 - f - mgsin28 = 0
    Fx = Fcos28 - ukN - mgsin28 = 0
    N = -(mgsin28 - Fcos28)/uk
    Fsin28 + mgcos28 = (-mgsin28 + Fcos28)/uk
    F = -mgsin28(1-uk) / (uksin28 - cos28)
    F = 245.5N

    W = F*d*cos(theta)
    W = 245.5N * 5.95 * cos28
    W = 1289.7

    I'm still getting the wrong answer, I must be making another mistake elsewhere

    thanks
     
  5. Dec 5, 2007 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Looks OK.
    Check this step.
     
  6. Dec 5, 2007 #5
    aha!
    got it

    thanks very much
    this problem was giving me much grief
     
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