You place your lunch leftovers in the refrigerator. Suppose the refrigerator nee
ID: 1470314 • Letter: Y
Question
You place your lunch leftovers in the refrigerator. Suppose the refrigerator needs to remove 1.3180E+4 J of thermal energy from your lunch to cool it to the temperature of the inside of the refrigerator. In the meantime, this means the refrigerator produces 1.6838E+4 J of thermal energy that it expels into the kitchen as a result. What is the total work done by the compressor motor in the refrigerator? (Ignore any thermal loses due to friction in the motor.)
3.658×103 J
What is the Coefficient of Performance for the refrigerator?
3.603
Your refrigerator actually acts like a heater in your kitchen. Suppose you have a small electric space heater that has a power output of 4.2kW. How long would this heater have to run to produce the same amount of heat as the refrigerator produced while cooling your leftovers?
4.009 s
HELP!! VVV
It takes electricity to run the motor on the refrigerator. If your cost of electricity is 9 cents per kilowatt*hour, how much does it cost (in cents - do not enter units) to cool your lunch down?
Explanation / Answer
QH = QC + W
1.6838 * 10^4 = 1.3180 * 10^4 + W
W = 3.658 * 10^3 J
COP = QC/W
COP = 1.3180 * 10^4 / 3.658 * 10^3
COP = 3.603
Cost = 9 cents per kilo watt hr
1 kwh = 3.6 * 10^6 J
1 J = 1/ (3.6 *10^6) Kwh
The total energy supplied by the electricity is the energy needed to cool the lunch plus the energy expelled as heat.
Total Energy = 1.6838 * 10^4 + 1.3180 * 10^4 = 3.0018 * 10^4 J
Total kwh used = 3.0018 * 10^4 * 1/ (36 * 10^6) kwh
Total kwh used = 0.000833 kwh
Total Cost = 9 cents * 0.000833
Total Cost = 0.0075 cents
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