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Homework Help: Heavy cart not moving but being pulled

  1. Mar 24, 2006 #1
    A person is sitting in a heavy cart with wheels. The person pulls a rope attached to a rigid support, but the cart does not move. Where does the energy expended by the person go?

    Is it converted into heat or stored somewhere as potential energy, please clarify?
  2. jcsd
  3. Mar 24, 2006 #2


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    What energy? If the cart doesn't move, no displacement -> no work done.

    He gets tired, sure, but that's his problem. He might as well use a pulley and attach mass to the rope so that it pulls on the rope with the same force. Same effect but now the guy doesn't get tired. No mechanical work is done.
  4. Mar 24, 2006 #3
    ''He gets tired, sure, but that's his problem. ''

    This is precisely what I meant to ask....

    What happens to the energy expended by the person [sure he expends some energy as he feels exhausted] as there is no work done.

    To put it in other words, try to lift a very heavy load off the ground [which you cannot say about 500 kg] and please clarify where do your 'efforts' to lift go. Some mechanical energy must be lost by you in form of movement of muscles [if you are really trying to lift]....
  5. Mar 24, 2006 #4

    Doc Al

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    Galileo is correct that no mechanical work is done on the cart or support, since neither moves. You seem to realize that energy is being used though. What do you think happens to the energy expended? And where does that energy come from, for that matter?
  6. Mar 24, 2006 #5


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    This is an excellent question, by the way.

    To answer this properly, one must start thinking about physiology....What happens when muscles are kept contracted...
  7. Mar 24, 2006 #6
    Can you expend Calories without doing any work?
  8. Mar 24, 2006 #7


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    Yes you can expand calories without doing any mechanical work. However, as nrqed says, if you look at physiology you see that heat is generated when muscles contract, heat is a form of energy and hence thermal work is done.

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