How do I calculate the equilibrium temperature of a system?

[chukie]

I've found the question that I am doing at this site:
http://www.kent.k12.wa.us/pcpow/questions/phys/0105Bird/index.html

The answer is given here, but not the steps:
http://www.kent.k12.wa.us/pcpow/solutions/physics/0105bird/index.html


I know how to do Part A, but no matter how I tried to do part B (What was the thermal equilibrium temperature of that coffee), I do not get the answer given 56.97 degrees C.

I've followed the instructions in the solution and setted the energy lost by the coffee to be equal to the energy gained by the ice and the cream:

I've attached my work:
http://img139.imageshack.us/img139/231/worklb2.th.png

Can someone tell me what I did wrong?

 

[Kurdt]

What you've done so far is fine. You need to expand the brackets and get all the final temps on one side and all the rest on the other. You've missed the specific heat capacity from some of the terms though.

 

[chukie]

What you've done so far is fine. You need to expand the brackets and get all the final temps on one side and all the rest on the other. You've missed the specific heat capacity from some of the terms though.

I did that but I got a value of -14194.9 =(

 

[Kurdt]

I'd check your working because using that method I get the answer. If possible write down all steps of your calculation so they can be checked.

 

[chukie]

I'd check your working because using that method I get the answer. If possible write down all steps of your calculation so they can be checked.

here's my work:
http://img523.imageshack.us/img523/162/42922872qx8.th.png

 

[Kurdt]

Like I said before you haven't included the specific heat capacity constant.

 

[chukie]

Like I said before you haven't included the specific heat capacity constant.

ahh i see! i assumed that the c's would cancel since they were all the same but i missed the fact that mL doesn't hv a c. thanks for your help!