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Homework Help: 3 masses, 1 pulley dynamics question

  1. Sep 29, 2008 #1
    1. The problem statement, all variables and given/known data

    mass 1 sits on a table, mass 2 sits on top of mass 1, mass 3 is connected to mass 2 via a string and pulley. (the pulley extends diagonally from the edge of mass 1)
    mass 3 is hanging beside mass1 and its side in full contact with mass 1.
    with what force must you push mass 1, such that mass 3 doesnt fall?
    all surfaces are frictionless.
    m1 = 10kg m2=5kg m3=8kg

    2. Relevant equations

    force of contact between 1 and 3 are the same in magnitude
    mass 1 moves because of the applied force, mass two because of the tension in the string, and mass three because it is contact with 1, and is being pushed by one.
    relative to each other, the masses dont move.

    3. The attempt at a solution

    i'm not sure how this can be done. i've tried several ways, but i dont understand what could keep mass 3 from falling.

    i really appreciate any help!
  2. jcsd
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