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Homework Help: Finding Joules of heat for 75% efficient motor at 250hp.

  1. Jan 22, 2012 #1
    1. The problem statement, all variables and given/known data
    Forgive me for any indiscretions my first post.

    The problem is to find the Joules of heat per hour produced in a motor that is 75% efficient and requires 0.250hp to run it.

    2. Relevant equations


    3. The attempt at a solution

    1. convert hp to Watts; 0.250hp* 746W/hp *75 percent=139W

    At this point the answer is wrong and I don't know why. I have tried for hours to solve this please help!
  2. jcsd
  3. Jan 22, 2012 #2
    Try multiplying by 25 percent instead. 75% efficient means that 25% of the applied work is converted to heat.
  4. Jan 22, 2012 #3
    I did the problem is that gives me a small number at around 48 the bok says the answer is 168KJ

    It's 139 when I multiply by 75%
  5. Jan 22, 2012 #4
    I don't know then. Would you mind typing out the problem exactly as it is stated?
  6. Jan 22, 2012 #5
    No problem.

    How many joules of heat per hour are produced in a motor that is 75.0 percent efficient and requires 0.250hp to run it? Ans 168kJ
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