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Homework Help: Work, Average Power, and Time?

  1. Oct 8, 2009 #1
    1. The problem statement, all variables and given/known data

    Determine the time it takes to climb three flights of stairs (height = 9.7m). Compute the work done against gravity. Compute the average power expended in watts and in horsepower.

    Person = 150lbs.

    2. Relevant equations

    h = 9.7m
    Avg Power = change in W/change in t
    1hp = 746W
    W = F * d

    3. The attempt at a solution

    Ok...so, my 150lb=667.5N. That's my F now.
    W = f * d = 667.5N * 9.7m = 6474.75J
    Once I can find the time it took, then I can use that and the work to find the average power. I just can't figure out how to get time traveled from Work done. Am I on the right track?
  2. jcsd
  3. Oct 8, 2009 #2


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    You are on the right track. Since the time is not given, you have to come up with a reasonable estimate or climb three flights of stairs and time yourself.
  4. Oct 8, 2009 #3
    Wow, that makes sense. (I had to measure the stairs myself to.)
    Thanks very much for replying so quickly!
    I got 21.33s
    Work = 5303.8J
    Power = 248Watts = 0.332hp
    That seems reasonable, right?
  5. Oct 9, 2009 #4


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    Pretty reasonable.
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