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Homework Help: Energy Efficiency: Input & Output (Work/Energy)

  1. Nov 4, 2013 #1
    1. The problem statement, all variables and given/known data

    In a race, a 54 kg athlete runs from rest to a speed of 11m/s on a flat surface. The athlete's body has an efficiency of 85% during the run. How much input energy did the athlete provide?

    2. Relevant equations

    efficiency = E out/E in x 100%

    3. The attempt at a solution

    I know E in = E out/efficiency
    and efficiency = 85%, m = 54 kg, vi = 0, vf = 11 m/s
    but how can I find E out?
    Eg = mgh ?
    There's no height though...?
  2. jcsd
  3. Nov 4, 2013 #2


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    Homework Helper

    His energy output is entirely kinetic! No need for a height.
  4. Nov 4, 2013 #3
    Oh, right.
    Could I use Ek = 1/2mv^2 to solve this then?
  5. Nov 4, 2013 #4


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    Homework Helper

    Yes you can :approve:
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