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Homework Help: Statics : find coefficient of static friction

  1. Nov 29, 2011 #1
    1. The problem statement, all variables and given/known data
    Find coefficient of static friction if shell starts to slip at θ = 60°

    known - θ
    unknowns - P, r, Normal force, weight

    2. Relevant equations
    friction = μ * normal force

    3. The attempt at a solution
    I do not know where to start. It looks like the picture wants you to assume P is always horizontal so it has no effect on the normal force which means friction is constant. If friction were constant though why would it start to slip?

    Attached Files:

  2. jcsd
  3. Nov 30, 2011 #2
    I haven't done this problem but here is a place to start.

    Find the centroid of the shell. The gravitational force will act through the centroid. P is horizontal. Do a free body diagram. Sum forces in X and Y direction. Sum the moments around the contact point. Hopefully everything falls out but Coefficient of static friction which is probably related somehow to the angle.
  4. Nov 30, 2011 #3
    Yep, the method I outlined above will give you the correct answer. Treat this as a statics problem.
  5. Nov 30, 2011 #4
    ah yes. Your method worked perfectly for me, thank you.
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