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Homework Help: Mechanical energy required each cycle to operate the refrigerator

  1. Sep 18, 2007 #1
    MODS close this thread down i figured out the answer myself

    1. The problem statement, all variables and given/known data
    A refrigerator has a coefficient of performance of 2.16. Each cycle it absorbs an amount of heat equal to 3.435×104 J from the cold reservoir.

    i need to find a) the mechanical energy required each cycle to operate the refrigerator.
    b)during each cycle how much heat is discarded to the high temperature reservoir.

    2. Relevant equations
    e = W/Qh; e=1+(Qc/Qh)

    3. The attempt at a solution

    i used the formula in b and apparently it isn't the answer. i also tried using 1-(Qc/Qh) to find Qh. it still didn't work. any other ideas?

    Last edited: Sep 18, 2007
  2. jcsd
  3. Sep 18, 2007 #2


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    Gold Member

    Well, the concept of a refridgerator is a device that moves energy from a cold reservoir to a hot reservoir. So, from this, you know the heat discarded in the hot reservoir has to be at least that removed from the cold reservoir. But you have to remember that you also have to put work into the system in order to get the heat to move from cold to hot, so there will be extra energy discarded into the hot reservoir that will be equal to the work put in. So can you find the total energy being dumped into the hot reservoir from this information?
  4. Sep 18, 2007 #3


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    Homework Helper

    The moderators aren't generally watching all these threads. I believe the local custom is that, if you are satisfied with the resolution of your problem, you can edit your thread title by adding [SOLVED] at the beginning.
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