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Simple Machines

  1. Mar 14, 2004 #1
    I totally do not understand how to do this. I missed this day in class and the teacher hasn't had time to explain it to me. Could someone help?

    The efficiency of a pulley system is 73%. The pulleys are used to raise a mass of 58 kg to a height of 3.0 m. WHat force is exerted on the string of the pulley systen if the string is pulled for 18.0 m in order to raise the mass of the required height?

    Thanks in advance
  2. jcsd
  3. Mar 14, 2004 #2


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    The way pullies work is by doing an equivalent amount of work by decreasing the amount of force needed and increasing the distance the force is applied over.
    work = work
    [tex]F_1d_1 = F_2d_2[/tex]

    Efficiency is always what you get out divided by what you put in. I'll use a little "e" to express efficiency.
    e = out/in
    e*in = out

    Now just fill in values

    [tex]eF_1d_1 = F_2d_2[/tex]

    [tex](0.73)F_1(18.0) = (58)(9.8)(3)[/tex]

    [tex]F_1 = 129.77[/tex]
    Last edited: Mar 14, 2004
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