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Engine efficiency

  1. Feb 14, 2007 #1
    An engine releases 0.490 kJ of heat for every 0.120 kJ of work it does. What is the efficiency of the engine?

    I am having trouble with this problem.
    I tried

    Wnet/ heat input = efficiency
    0.120/0.450 = 0.27
    but it says it is the wrong answer. (correct answer is 0.21)
  2. jcsd
  3. Feb 14, 2007 #2


    User Avatar

    Staff: Mentor

    The efficiency is the useful work divided by the total energy. What is the total energy in terms of the useful work and the waste heat generated?
  4. Feb 14, 2007 #3

    0.120/(0.450+0.120) = 0.211
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