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Homework Help: Internal energy of the gas in a gasoline engine

  1. Apr 28, 2007 #1
    I am so lost with this question. Can anyone help?

    The internal energy of the gas in a gasoline
    engine's cylinder decreases by 176:7 J.
    If 67.0 J of work is done by the gas, how
    much energy is transferred as heat? Answer
    in units of J
     
  2. jcsd
  3. Apr 28, 2007 #2
    Use the first law of thermodynamic:
    Q=U+W, where W is the work done by the gas
     
  4. Apr 28, 2007 #3
    I did Q= 176.7 (change in energy) + 67 (amount of work done)

    I got 243.7
    What am I doing wrong
     
  5. Apr 28, 2007 #4
    I think the mistake is here.
    Q=U+W but since the work is fone by the gas the the +w might be deceiving.
    W is positive if work is done on the gas.Since instead it is done by the gas it would imply you will have to add -67
    Therefore the answer is 176.7-67=109.7
     
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