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Homework Help: Heat problem

  1. May 11, 2005 #1
    An engine with an output of 150W has an efficiency of 25%. It works at 10 cycles/s.

    A. How much work is done in each cycle?
    work=power(delta t) = 150 W * 1s = 150 J
    work =15.0 J per cycle

    **got part A correct

    B. How much heat is given off in each cycle?
    delta internal energy = delta work + delta heat
    delta intergy = 0 bc its a complete cycle
    delta heat = - delta work
    delta heat = 15 J

    **Part B isn't coming out.....please guide in the correct direction if possible.
  2. jcsd
  3. May 11, 2005 #2

    Doc Al

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    Staff: Mentor

    Realize that what you are calling "delta heat" equals [itex]Q_{in} - Q_{out}[/itex]. What you need to find is [itex]Q_{out}[/itex]. Also recall the definition of efficiency: [itex]\eta = W_{out}/Q_{in}[/itex].
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