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Sliding blocks and a string problem

  1. Mar 7, 2017 #1
    1. The problem statement, all variables and given/known data

    Block A, with weight 3w, slides down an inclined plane S of slope angle 36.9 degrees at a constant speed while plank B, with weight w, rests on top of A and is attached by a cord to the wall. If the coefficient of kinetic friction is the same between A and B and between S and A, determine its value.

    2. Relevant equations

    3. The attempt at a solution
    I have some trouble doing the free body diagram for A, I assume the forces acting on said block are: NB, wA, static friction between S and A, but Im not sure about the friction between A and B.
  2. jcsd
  3. Mar 7, 2017 #2


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    You mention static friction between S and A, but not the normal force there.
    Why do you doubt friction between A and B, yet have listed "NB", which I take to be the normal force between A and B?
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