# Homework Help: Thermal Question, I seem to be doing something wrong

1. Jul 19, 2004

### Brianjw

Well I swear I am doing this right but something seems that its the wrong answer as the website I enter it into is rejecting it. If you see a flaw in my methods let me know:

The two ends of an insulated metal rod are maintained at a temperature differential of 100 degrees C . The rod has a length of 73.3 cm and a cross-sectional area of 1.06 cm^2. The heat conducted by the rod melts a mass of 7.80g of ice in a time of 11.3 min

So what I did was first find the amount of energy required to melt the ice without changing the temperature which uses Q = m*L

therefore:

$$.0078kg * 3.34 * 10^5 J/Kg = 2605.2$$

then I use the formula:

$$H = Area*k*(T_h - T_c)/L$$

I need to find k for the answer in terms of W/m*k

So since H = dQ/dt I get, 2605.2/11.3 = 230.549
Using the above forumla and converting Celcius to Kelvin I have:

$$230.549J/min = .000106 m^2 * k * 373.15K/.733m^2$$

which gives me approx 4270. Can anyone see where I went wrong?

Thanks

2. Jul 19, 2004

### Staff: Mentor

For some reason you treated the temperature difference as if it were a temperature that needed converting. No need to "convert": 100 C-degrees = 100 K-degrees.

Another problem: measure heat flow in J/sec, not J/min.