Thermodynamics and ice melting.

[Terp]

[SOLVED] Thermodynamics and ice melting.

Homework Statement

An open container holds ice of mass 0.585 kg at a temperature of -13.3 *C. The mass of the container can be ignored. Heat is supplied to the container at the constant rate of 800 J/min.

The specific heat of ice to is 2100 J/Kgand the heat of fusion for ice is 334x10^3 J/Kg.

Homework Equations

Q=cm\Deltat
Q=mLf where Lf = fusion for ice

The Attempt at a Solution

The first part asks:

How much time t_melts passes before the ice starts to melt?
I got the answer to this to be 20.4 minutes and I know it's correct. I used Q=cm\Deltat= 1.63x10^4 J, where(c = 2100, m=.585, delta T = 13.3). I then used the rate of 800J/Min to get 20.4 min.

The second part asks:

From the time when the heating begins, how much time t_rise does it take before the temperature begins to rise above 0 *C?

I'm absolutely stumped. It's probably very simple and right over my head. The hint for the problem had me find how much time it'd take to melt once it got to 0*C and I found that to be 244 minutes (using Q = mLf, then Q / 800J/min to get time), which is correct.

I feel like these two are the same question, since for the first one I'm finding the time it takes for the ice to start melting, which is at 0*c. Anybody have any clue? I've tried 20.4 min and 223.6 min and Mastering Physics tells me they're both wrong. Thanks a lot!

 

[kamerling]

The time doesn't start to rise until all the ice has melted. So you just need the sum of both times you already calculated.

 

[Terp]

So you're saying that the temperature won't start to rise over 0 until the ice has all melted? Seems like there could be other variables in play. That was the answer though, thanks a lot :). So simple it went right over my head.