[toospooky]

I haved worked this problem and emailed my instructor and still I am having trouble. If someone could point me in the right direction I'd appreciate it.

The question is:
Find the heat flow in 25.0 days through a freezer door 80.0 cm x 144 cm insulated with cellulose (0.039 J/smC) fiber 4.0cm thick. The temperature is -14 C. Room temp is 22C.

Here is what I used.
t= 25.0 days = 2.16 x 10^6 s
L= 4.00 cm = 0.04 m
A= 80.0 cm x 144 cm = 11520 cm^2 = 1.152 m^2
T1= -14C
T2= 22C 22C-(-14C)=36C
Q=?

Using the formula Q= KAt(T2-T1) / L

Q= (0.039 J/smC) ( 1.152m^2) (2.16x10^6s) (36C) / 0.04 m
My answer is 8.73 x 10^7

The answer should be 2.4x10^4 J or 24 kJ

[Unknown008]

I can't find anything wrong. I don't know that formula, but if that's the right one, your answer should be correct and the supposed answer not.

[jcaron2]

Assuming the k-value for cellulose is realistic, I have a much easier time believing your answer than the supposedly "correct" one. Yours equates to around 24 kWh of energy per month. The other answer amount to only around 0.007 kWh per month. That's a kWh every 12.5 years. That would be one heck of an efficient freezer!

The supposedly "correct" answer seems like it was accidentally calculated with K in J/mC per hour, instead of J/mC per second.

[toospooky]

Thank you for those who looked at this problem. I contacted my instructor again about the problem. He finally emailed me back saying the book answer is incorrect. The answer I came up with is indeed the right answer. Thanks again.