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Wall excerts work on skater: Please help

  1. Jun 15, 2009 #1
    Wall excerts work on skater: Please help :(

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

    A 69.0-kg short-track ice skater is racing at a speed of 11.0 m/s when he falls and slides into a padded wall that brings him to rest. Assuming that he does not lose any speed during the fall or while sliding across the ice, how much work is done by the wall while stopping the ice skater?



    2. Relevant equations
    Ke=1/2mV^2
    W=1/2m(Vf^2+Vi^20
    W=Fdcos()
    F=ma or F=mg


    3. The attempt at a solution

    I am not sure what I am doing. I attached an image of my work.
     

    Attached Files:

  2. jcsd
  3. Jun 15, 2009 #2

    PhanthomJay

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    Re: Wall excerts work on skater: Please help :(

    is this the work-energy theorem equation? It's not correct, but this one looks like the one to use, once corrected. Can't see your work yet, though.
     
  4. Jun 15, 2009 #3
    Re: Wall excerts work on skater: Please help :(

    W=1/2m(Vf^2+Vi^2)
    W=1/2(69)(0^2+11^2)
    W=1/2(69)(121)
    W=34.5(121)
    W=4174.5
    This is wrong answer.
     
  5. Jun 15, 2009 #4

    PhanthomJay

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    Re: Wall excerts work on skater: Please help :(

    check your work energy equation again; it is incorrect. And don't forget the units.
     
  6. Jun 15, 2009 #5
  7. Jun 15, 2009 #6
    Re: Wall excerts work on skater: Please help :(

    W=1/2mVf^2-1/2mVi^2
    W=1/2(69)(0)-1/2(69)(121)
    W=-4174.5 J
     
  8. Jun 15, 2009 #7

    PhanthomJay

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    Re: Wall excerts work on skater: Please help :(

    Looks good now!
     
  9. Jun 15, 2009 #8
    Re: Wall excerts work on skater: Please help :(

    Thanks ^^
     
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