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A tough pulley cable system problem!

  1. Apr 3, 2009 #1
    1. The problem statement, all variables and given/known data
    In the pulley-cable system shown, the acceleration of block A, x(double dot), varies with time, t(in seconds), as given by the expression x(double dot) = 2t m/s2. initially the two blocks are 5m apart and both are stationary.

    http://img3.imageshack.us/img3/2074/pulleycable.jpg" [Broken]


    i)what is the acceleration, y(double dot), of block B at time t?
    ii)what is the velocity of block B when t = 3s?
    iii)how far apart are the blocks when t = 3s?
    2. Relevant equations

    F= ma
    Length of rope = constant


    3. The attempt at a solution

    F=maaa
    2 T = ma2t
    T = mat

    F=mbab
    3/2 T = mbab
    3/2 mat = mbab
    ab = (3mat)/(2mb)

    is it correct for part (i)?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 3, 2009 #2

    turin

    User Avatar
    Homework Helper

    I don't think that you need Newton's second law. Is the pulley on the left, closer to B, fixed to B or fixed in space?
     
  4. Apr 3, 2009 #3
    What you really have here is a kinematics problem. You need to express the fact that the length of the rope remains constant, in terms of x and y. Until you do that, nothing is going to happen.
     
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