1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    rock.freak667

    User Avatar
    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

    rock.freak667

    User Avatar
    Homework Helper

    Yes you can :approve:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Loading...