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Work, Energy, Power Problems: No Mass? No Speed?

  1. Nov 5, 2013 #1
    1. The problem statement, all variables and given/known data

    Athletes who compete in downhill skiing try to lose as little energy as possible. A skier starts from rest at the top of a 65 m hill and skis to the bottom as fast as possible. When she arrives at the bottom, she has a speed of 23 m/s. Calculate the skier's efficiency. Explain why the mass of the skier is not required when calculating the efficiency.

    2. Relevant equations

    Eg = mgh

    3. The attempt at a solution

    I don't understand since Eg = mgh, and I'm only given height and velocity. How could I possibly find the skier's efficiency without mass?

    *Also, another question asks how I could determine power without time. How is this possible when P = E/t?
  2. jcsd
  3. Nov 5, 2013 #2


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    Science Advisor
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    Gold Member

    Just put the mass in as an unknown m and plod through the equations. See what happens.
    For the other question, you need to post it in full.
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