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Homework Help: This seems too simple?

  1. Jan 28, 2010 #1
    1. The problem statement, all variables and given/known data
    A man pumps water at a rate of 20 liters per minute to a height of 10 meters. How much work does he do in an hour? Friction is to be neglected. A liter of water is taken to weigh 1 kilogram.

    2. Relevant equations

    3. The attempt at a solution
    If 1 liter=1 Kilogram then 20 liters = 20 kg
    Work is a kind of energy conversion. The work done per unit of time is
    P= ΔE/ ΔT = (20)(9.8)(10)/(60minutes) = 32.67J/minute

    Is this correct? I'm unsure about the conversions?
  2. jcsd
  3. Jan 29, 2010 #2
    Your answer for the power is correct, but you should divide by 60 seconds, not 60 minutes, and the answer would then be in J/s, or W You need to multiply that with the number of seconds in an hour to get the answer to the question.
  4. Jan 29, 2010 #3
    So the correct answer would be:
    P = ΔE/ ΔT = (20)(9.8)(10)/(60seconds) = 32.67J/seconds
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