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Homework Help: Friction question, maximum incline

  1. Jun 5, 2013 #1
    1. The problem statement, all variables and given/known data

    An object of mass 50kg rests on a rough plane incline at an angle alpha to the horizontal. It is supported in this position by a light string parallel to the plane. The string has a breaking strain of 200N and the coefficient of friction between the object and the plane is 0.2. Find the largest value of alpha for the string to remain intact.

    3. The attempt at a solution

    Resolving parallel to the plane:

    50gsin(alp) = 200 + (0.2x50gcos(alp))
    = 200 + 10gcos(alp)

    So it seems that I have to find the maximum value of alpha for which the above equation is true, but I have no idea how to do that.

    Any help would be much appreciated. Thanks :)
  2. jcsd
  3. Jun 5, 2013 #2
    why not take sin(α)=x and cos(α)=√(1-x2)
  4. Jun 5, 2013 #3


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    Gold Member

    You can rewrite as $$50g \sin \alpha - 10 g \cos \alpha = 200$$ and express the LHS as one trig function and a corresponding phase.
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