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Homework Help: Electrical power

  1. May 1, 2010 #1
    Hi:
    Would somebody please check to see if I am on the right track with this problem.
    Many thanks

    1. The problem statement, all variables and given/known data
    An 80kg man on a step-exercise machine climbs a staircase 3.0m high in 8.5s. If he works at the same rate to drive a pedal-operated generator with an efficiency of 75%, how much electrical power would be produced?



    2. Relevant equations
    power=work done/time taken
    efficiency=useful energy output/total energy input
    work=force x displacement in direction of force
    F=ma
    weight=mg (gravity=10ms ^-2)



    3. The attempt at a solution
    F=80 x 10 =800N
    Work done (W)=800 x 3.0 = 2400J
    Power=2400/8.5 = 282.4W (1d.p.)
    therefore
    75% x 282.4 = 211.8W
    F=
     
  2. jcsd
  3. May 1, 2010 #2
    looks good
     
  4. May 2, 2010 #3
    thank you
     
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