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Another ramp question

  1. Oct 16, 2005 #1


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    This question is driving me nuts. I really need help with it, actually i just need help setting up my equations.

    Mu = the weird friction sympol

    A box of a mass m=22 kg is at rest on a ramp inclined at 45 degrees to the horizontal. The coefficient of friction between the box and the ramp are "Mu s" = 0.78 and "Mu k" = 0.65.
    a)Determine the magnitude of the largest force that can be applied upward, parallel to the ramp, if the box is to remain at rest.

    My equation are:

    Fn=Fgy - Fapp
    Fnet = 0
    Fnet = Fgx - Ffs

    After that i end up getting two equations for Fapp but when i solve for it i get a negative answer. I also tried flipping Fapp so Fn=Fapp - Fgy but that also won't work, i get the wrong answer.

    So can anyone please help get my two equations, theres something wrong with mine.
  2. jcsd
  3. Oct 16, 2005 #2


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    Homework Helper

    Please clarify your expressions, what is Fn, what are Fapp and Ffs?

    Which way does the friction act?
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