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Homework Help: Torque and frictional force

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  1. Mar 1, 2015 #1
    1. The problem statement, all variables and given/known data
    In the picture

    2. Relevant equations
    Torque = I * Alpha 10951894_10200266867310554_1551086073_n.jpg
    Alpha = a / r
    Fnet = m*a

    3. The attempt at a solution
    I provided my work in the pictures. I figured out that the frictional force in system B is greater than in system A. I am not sure how to compare this with the frictional force from system C. I figured out the sum if the frictional forces of A and B are equal to mg sin theta, but don't know how the two compare.
     
  2. jcsd
  3. Mar 1, 2015 #2

    TSny

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    Answers to (a) and (b) look good to me. According to (b), objects B and C have the same net force. Look at your free body diagrams for objects B and C. If you add the forces in the diagram for B do you get the same net force as the diagram for C?

    What should be the direction of the friction force on C to make it rotate in the right direction for rolling down the plane?
     
  4. Mar 1, 2015 #3
    So Friction force on C is pointing up the ramp and its magnitude is equal to friction force on B? The frictional force on C is kinetic not static correct?
     
  5. Mar 1, 2015 #4

    TSny

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    Yes, that's the only way Fnet,B can equal Fnet,C.

    To answer this, remember that the statement of the problem says that C rolls without slipping.
     
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