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Am I Doing this Right? Specific heat capacity questions sheet Watch

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    Hi,

    In my physics homework there is the following question:

    It is sometimes said that the cost of running an upright freezer is greater than the cost of running a chest freezer because each time the door of an upright freezer is opened the cold air falls out. Consider an upright freezer of 0.2m^3 and discuss whether there is any truth in this statement. The temperature inside a freezer may be assumed to be about -18 degrees C and the specific heat capacity of air under these conditions is 600Jkg^-1K^-1.

    The given answer is about 5kJ lost but I got 6.6667J
    Here's what I did:
    0.2m^3 = 200000cm^3 and 1m^3 of air weighs 1.292kg so 1.292/5 = mass of 0.2m^3 = m = 0.2584kg
    c = 600Jkg^-1K^-1 = 0.6kJkg^-1K^-1
    T = -18 in the freezer so if RTP is 25 then the change in T= 43
    Change in Q = 0.6 * 0.2584 * 43 = 6.6667J

    Thanks in advance for any help
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    don't suppose you know how to do this one too do you? the bear
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    the density of air is greater at low temperatures...

    at -20 C the density is 1.395 kg/m³*
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    (Original post by the bear)
    the density of air is greater at low temperatures...

    at -20 C the density is 1.395 kg/m³*
    Ah, I knew it was denser but couldn't find a value, thank you very much!
 
 
 
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