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Homework Help: Work done pulling up a curtain

  1. May 21, 2010 #1

    Uku

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    1. The problem statement, all variables and given/known data

    A curtain is rolled up a thin rod. There is no friction. The length of the curtain is l=2m and weight is m=2kg. Find the work done.

    EDIT: the mass is 1kg not 2.

    2. Relevant equations

    A=Fs

    3. The attempt at a solution
    The solution is A=9.81J The way I did it was that the work done is the area under the curve on the F/s plot. Since the force needed to pull drops linearly, I simply multiplied mg*l and then I divided that by two. Is this approach valid? The answer is correct.
     
    Last edited: May 21, 2010
  2. jcsd
  3. May 21, 2010 #2
    mg*L/2 equals 19.6 J are you saying that 9.81 J is supposed to be the correct answer? I assumed that the center of mass of the curtain was at L= 1 m and that mass was lifted 1 meter to the top of the window. Work = Force * distance * Cos(0)
     
  4. May 21, 2010 #3

    Uku

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    I mistyped the mass, it is 1kg.
     
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