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Homework Help: Work-energy theorem please help, not sure what I am doing wrong.

  1. Feb 15, 2010 #1
    On an essentially frictionless, horizontal ice rink, a skater moving at 6.0 m/s encounters a rough patch that reduces her speed by 42 \% due to a friction force that is 20 \% of her weight.

    Use the work-energy theorem to find the length of this rough patch.

    i do: [.42 * (.5) * (6)^2]/ [.2 * 9.8]=3.85
    but i get the wrong answer can anyone help, does the answer need to be negative, what am i doing wrong.
     
  2. jcsd
  3. Feb 15, 2010 #2

    ehild

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    What does the work-energy theorem state?

    What is the change of the KE if the speed is reduced to 42% of the original 6 m/s ?

    ehild
     
  4. Feb 16, 2010 #3
    K_2-K_1 where k=1/2*m*v^2, thank you, it would be .58v not .42, in the equation
    -.2gs = (1/2)mvf^2 - (1/2)mvi^2 where the m cancel
     
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