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

1. 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
2. don't suppose you know how to do this one too do you? the bear
3. the density of air is greater at low temperatures...

at -20 C the density is 1.395 kg/m³*
4. (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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