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Homework Help: Newton's Second Law and Friction

  1. Oct 11, 2009 #1
    1. The problem statement, all variables and given/known data

    Block A weighs 1.14 and block B weighs 3.66. Block A rests on top of block B and has a cable connecting it to the wall on its right. The coefficient of kinetic friction between all surfaces is 0.300. Find the magnitude of the horizontal force necessary to drag block B to the left at constant speed if A is held at rest. (See Figure B)

    2. Relevant equations

    Fnet = ma
    Fnet = 0

    3. The attempt at a solution

    I think that I am just getting the forces on the free body diagram wrong. I drew FBDs for block B and block A and got that Fnet = 0, and so the horzontal force plus force friction by block A minus force friction by the ground equals 0. And I got F = FfG-FfA. What have I done wrong?

    Attached Files:

  2. jcsd
  3. Oct 11, 2009 #2


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    Homework Helper

    Hi am13, welcome to PF.
    The frictional force acting on A is towards right.
    Reaction to this force on B acts towards left.
    Applied force on B is towards left.
    Frictional force on B acts towards...?
    What is the condition for the constant velocity of B?
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