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Window washer

  1. Jul 11, 2009 #1
    1. The problem statement, all variables and given/known data
    A window washer of mass M is sitting on a platform suspended by a system of cables and pulleys as shown . He is pulling on the cable with a force of magnitude F. The cables and pulleys are ideal (massless and frictionless), and the platform has negligible mass.Find the magnitude of the minimum force F that allows the window washer to move upward.
    Express your answer in terms of the mass M and the magnitude of the acceleration due to gravity g.
    MFS_1l_18_001.jpg


    2. Relevant equations

    Newton's second Law

    3. The attempt at a solution

    For the person: Ma = F + T -Mg where T is the tension in the cable holding the platform and F is the force of the rope on the washer.

    Then from the lower washer T = 2T[tex]_{1}[/tex], where T[tex]_{1}[/tex] is the tension in the rope

    So Ma = F + 2T[tex]_{1}[/tex] - Mg

    The block is about to move so Ma = 0 and I think T[tex]_{1}[/tex]=F so then

    0 = 3F - Mg

    I am not sure about this though
     
  2. jcsd
  3. Jul 12, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me. :smile:
     
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