Thermodynamics Block of Copper Problem

[flythisforme]

Hi, I need help with this problem for physics. I know it has something to do with Q=mcT. I can probably do parts b and c if I just get a start on part a. I'm just not sure how to approach it. Any help is appreciated. =)

A 50g block of copper having a temperature of 400K is placed in an insulating box with a 100g block of lead having a temperature of 200K. a) What is the equilibrium temperature of this two-block system? b) What is the change in the internal energy of the two-block system as it goes from the initial condition to the equilibrium condition? c) What is the change in the entropy of the two-block system?

Thanks in advance,
Cara

 

[dextercioby]

Actually part a) is the simplest.Compute the heat each body need to change (either accept or receive) in order to reach equilibrium.Then use the "insulating box" part...

Daniel.

 

[flythisforme]

Well I just calculated that the initial heat of the copper is 7720J and the initial heat of the lead is 2560J, but how would I calculate how much heat they need to accept or receive in order to reach equilibrium?

 

[dextercioby]

U have a copper block at 400K and this cools till he reaches equilibrium temp:x (unknown).

The heat lost is

$$Q_{lost}=m_{Co}c_{Co}\left(400-x\right) \ [J]$$

The lead block heats from 200K till equilibrium temp."x".

The heat received

$$Q_{received}=m_{Pb}c_{Pb}\left(x-200\right) \ [J]$$


What is the connection between the 2#-s (i used no sign convention:both #-s are positive (i hate sign conventions in thermo & geom.optics)) ??

Daniel.

 

[flythisforme]

Sorry I stopped posting after. I had to run out really quick unexpectedly. I did what you said and I got 794K as an equilibrium temperature, but that doesn't make sense. Maybe I did it wrong? You probably aren't there anymore but if you aren't, if someone else wants to help me that would be awesome.

 

[flythisforme]

actually I take that back, I got 317K now. So then would that be the answer for part a?

Also, when I do get the equilibrium temp. for part (a), for part (b) would I find the change in internal energy for each block and add the two values together? And as far as finding that, what would be the best equation to use?

would I use an internal energy equation for an isochoric system?

 

[flythisforme]

I'm just trying to get this thread back up higher since I'm not getting any responses. I still need some help. I'd really appreciate it!