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Homework Help: Pulley System

  1. Jun 17, 2007 #1
    1. The problem statement, all variables and given/known data
    A pulley system has an efficiency of 76.9%. The acceleration of gravity is 9.81 m/s^2. How much of the rope must be pulled in if a force of 620 N is needed to lift a 52 kg desk 2.32 m?

    2. Relevant equations
    Force = ma
    Work = force * distance

    3. The attempt at a solution
    Because the efficiency is 76.9%, I divided 620 N by .769 to find the amount of force that the pulley system would actually have to do. (806 N). I then found the amount of work required to lift the desk without the pulley system. 52 kg * 9.81 m/s^2 * 2.32 m = 1182.87 J
    To find the distance the rope has to be pulled in, I used the work formula.
    1182.87 J = 806 N * (distance)
    distance =1.47 m

    Pulley problems have never been my forte and I'm not sure if my attempt at this problem was right. Any help would be much appreciated!
  2. jcsd
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