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Homework Help: Can sum1 help me wit this question?

  1. Jan 10, 2005 #1
    hey can sum1 help me with this question?

    a swimmer is trying to swim upstream in a river with a constant flow of water, but remains stationary relative to shore.

    a. is any work being done on the swimmer? explain.

    b. if the swimmer stops swimming and floats with the water flow, is any work done on the swimmer? Explain.

    plz get back to me asap. im studyn for my test

    email be back at b_ball_gurl87@hotmail.com
  2. jcsd
  3. Jan 10, 2005 #2
    a very good way to test any work being done on the swimmer is simply asking him, " are you tried ?" if he did, he must have DONE some WORK...
  4. Jan 11, 2005 #3


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    Start with the definition of work.

    (Constant force case)
    The work done on an object as it travels from one point to another is the force times displacement.

    Suppose you're standing on the shore. What is the displacement of the swimmer? So what is the work done on the swimmer?

    No. This is a common misconception about the concept of work. Do not relate work with physical labour.
    Suppose you would hold a heavy book in one hand with outstreched arm. You'd get pretty tired after a while, but since the displacement of the book is zero, NO work is done on the book.
  5. Jan 11, 2005 #4


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    Very good. Just like the situation when a person pushes against an immovable wall.

    But can you figure out why a person gets tired if no "work" is actually being done ? (hint : consider micro-scale effects)
  6. Jan 11, 2005 #5


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    The original question also did NOT ask if the person had done work. It asked if work was done ON him.

    As long as he is stationary, there is no work done on him. If he floats downstream, then work is done on him.
  7. Jan 11, 2005 #6

    lol :biggrin:
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