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Homework Help: Movable pulleys and force

  1. Jun 14, 2009 #1
    1. The problem statement, all variables and given/known data

    In the figure below, the man and the platform together weigh 780 N. The pulley can be modeled as frictionless. Determine how hard the man has to pull on the rope to lift himself steadily upward above the ground.



    2. Relevant equations

    I didn't use any until it said i was wrong but here is what it would be:

    mg = T(1) + T(2)
    T(1) = T(2)

    3. The attempt at a solution

    mg = 780 N = 2*T(1)

    780 N / 2 = T(1)

    390 N = T(1)

    I first entered 390 and it was wrong, then I tried 391 to steadily move it upward. Both were wrong. Any help?

    Attached Files:

  2. jcsd
  3. Jun 14, 2009 #2
    cant anyone help
  4. Jun 14, 2009 #3
    I believe the answer is simply T = 780 N.

    T - mg = m(0)
    T = mg = 780 N

    They didn't give you any value for the acceleration which if they did would've changed alot.
  5. Jun 14, 2009 #4
    nevermind i figured it out, thanks
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