# Thermodynamics - First law Q

1. Apr 8, 2015

### DrVirz

1. The problem statement, all variables and given/known data
Hi all, please see uploaded pics. I can do the first 3 questions but can't get my head around the 4th. Any help is appreciated.

2. Apr 8, 2015

### Delta²

The rate at which heat is lost by the air $P_{air}$, equals to minus the rate $P_{water}$at which heat is absorbed by the water. So it will be $P_{air}=-P_{water}$.

$P_{air}=C_{air}\dot{m}_{air}(47-167)$, $P_{water}=C_{water}\dot{m}_{water}(40-35)$

3. Apr 8, 2015

### DrVirz

Hi Delta,

What have you denoted as C?

4. Apr 8, 2015

### Delta²

Its the specific heat capacity. For water is 4.17 and for air around 1.01 at the temperatures of this problem.

5. Apr 8, 2015

### DrVirz

I thought it was the specific heat capacity but I can only find the Cv/Cp for water in any of the tables from my text which was confusing me a bit.

Cheers for the help!

6. Apr 8, 2015

### Staff: Mentor

It's liquid water. What is the heat capacity of liquid water?

Chet

7. Apr 8, 2015

### DrVirz

Sorry in my previous post i meant to say CANT find the Cv/Cp value for water in any of my tables.

8. Apr 8, 2015

### Staff: Mentor

The heat capacity of liquid water is 4.18 kJ/kg C. Did you not see Δ2's post # 4? Are you saying you never had this in freshman physics?

Chet

9. Apr 8, 2015

### DrVirz

Yes I did see that in Delta's post. I am just saying, naturally, I refer to the tables for my data values and when I didn't come across a value for water it threw me off. I thought I had done something wrong. That's what happens when you have been studying all day I guess, time to take a rest.

10. Apr 8, 2015

### Staff: Mentor

All I did was Google "heat capacity of water."

Chet