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Homework Help: Question involving LAWS OF WORK

  1. Nov 7, 2006 #1
    I have been given the prompt:

    "Using a set of pulleys, a mover raises a 1000-N crate a distance of 5.00 m. This is accomplished by pulling in 20.0 m of cord"

    I need to find

    • How much effort would have to be applied if this were an ideal machine
    • If the effort actually applied is 300 N, what force is used to overcome friction?
    • What is the work output?
    • What is the work input?
    • What is the real mechanical advantage?

    I don't know if I have done this correctly so if someone would be willing to verify my answers or guide me through this, it would be appreciated.

    1. In an ideal machine, I believe work input is equal to work output. With that being said, I can set up the equation 1000N * 5.0 M = XN * 20.0 M, then I can solve X for 250 N... Correct?

    2. I'm not too sure what it means when it asks to OVERCOME friction, so what do i do?

    3. Work output is just equal to force * distance, so we evaluate the given 1000N force times the given 5.0 M distance and get 5000 J, Correct?

    4. Work input is just equal to force * distance as well, so we evaluate the value we solved for in number 1 (250) and multiply by the given 25 m distance and get 5000J, correct?

    5. Not sure at all what to do :confused:
  2. jcsd
  3. Nov 7, 2006 #2


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    5. Ideal MA is 4, since it took just 1/4 of the weight to move it (250/1000 =1/4). So its actual MA is??
  4. Nov 7, 2006 #3
    alright man, I understand it. Thanks SO much
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