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How to calculate average power in this case?

  1. Apr 6, 2013 #1
    1. The problem statement, all variables and given/known data
    A runner is rises up by 4.5 meters in 3.5 seconds, what average power must be consumed?


    2. Relevant equations
    P=w/t
    w=F.d


    3. The attempt at a solution
    p=4.5/3.5= 1.28 watt
     
  2. jcsd
  3. Apr 6, 2013 #2
    Average power is work done divided by time taken, as you've correctly written: P = W/t.

    But you have substituted in a distance for W; this is incorrect, W is the work done and is measured in joules.

    What has the runner done work against? What type of energy has changed?
     
  4. Apr 6, 2013 #3
    thats exactly what i wanted to ask, as we know w=f.d here we can use d=4.5m but what about F?
     
  5. Apr 6, 2013 #4
    What force is acting on the runner (there's only one :) )?

    I've just realised there's no mass - you can't get a numerical answer without knowing the mass of the runner. Did you not get given a value for the mass?
     
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