Need help with multiple choice questions

  • #1
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Ok guys, I’ve got a few multiple choice questions I need help with. Here they are, and thank you in advance!!!


All I know for this one is……Ql/Qh = Tl / Th Leaning towards B.
1. In a Carnot cycle
A. Qh > Ql * Th/Tl
B. Qh = Ql * Th/Tl
C. Qh < Ql * Tl/Th
D. Qh = Ql * Tl/Th

We are able to choose our own answer too, if none are correct below. I don’t think any of them are correct, so I chose Cp – Cv = R. If one of them is correct, I need to know. I’m thinking of choosing B.
2. For an ideal gas:
A. Cp = Cv
B. Cp > Cv
C. Cp < Cv
D. Cv = Cp + R

And, finally……I have this work problem.

3. Bill drops a 50 gram (0 deg C) ice cube into a large pond which is at 20 deg C. What is the total entropy change of the total process?

I found the change in the pond to be -71 J/K. So wouldn't the ice cube be 71 J/K, making the total process be zero??? Or I also figured it to have the ice cube be about 5.4 J/K larger.

Thanks,
Brad
 
Last edited:

Answers and Replies

  • #2
lightgrav
Homework Helper
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1) Ever hear of a reciprocal (1/x)? Qh/Ql = Th/Tl , so Qh = ...
2) So, if Cp - Cv = R , what is Cp ? Is this "R" positive or negative?

3a) What is the Temperature [K] of the ice as it melts?
What Q enters it meanwhile? Compute its entropy change (SIGN!)
3b) What is the Temperature of the pond as the ice melts?
What Q leaves the pond meanwhile? Compute its entropy change (SIGN!)
 

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