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Homework Help: Finding out coefficient

  1. Nov 4, 2012 #1
    1. The problem statement, all variables and given/known data

    A coin of mass m is at rest on a book that has been tilted at an angle θ with the horizontal. By experimenting, you find that when θ is increased to 13o, the coin is on the verge of sliding down the book, which means that even a slight increase beyond 13o produces sliding. What is the coefficient of static friction μs between the coin and the book?

    2. Relevant equations

    F=ma, f(static friction) = (μ)*normal force

    3. The attempt at a solution

    I drew out the problem, but from here I am sort of lost.
  2. jcsd
  3. Nov 4, 2012 #2


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    Staff: Mentor

    The weight of the coin is a force downwards, right? Rewrite that force as the sum of a force perpendicular (normal) to the surface of the book and parallel to the surface of the book. The parallel force is trying to make the coin slide; it's opposed by the force of friction, which is related to the normal force.
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