# How much work?

1. Jan 8, 2016

### kent davidge

1. The problem statement, all variables and given/known data

2. Relevant equations

no

3. The attempt at a solution

no

Since the problem asks how much work was done by OR on the gas, I did not understand why the book's answer is 162 J instead ±81 J that I've found. (sorry my bad english)

Sorry, the correct question on the problem is how much work was done from b to c instead from a to b as it's in the image.

Last edited by a moderator: Jan 8, 2016
2. Jan 8, 2016

### Isaac0427

Show us how you got your answer, then we can point out what you did wrong. Also, be careful with your units. I don't know all the unit conversions but to use Joules the units for P and V are pascals and meters cubed, not atmospheres and liters.

3. Jan 8, 2016

### kent davidge

Okay.

dW = dV p

In this case we have the initial and final values of V and p. So, W = (Vc - Vb) x 10-3m³ x (Pc - Pb) x 1.013 x 105Pa, wich gives W = 81.04 J.

4. Jan 8, 2016

### haruspex

You have calculated $\Delta V\Delta p$. That is not the same as $\int p.dV$.

5. Jan 8, 2016

### kent davidge

and how can I solve the integral for T?

6. Jan 8, 2016

### haruspex

In the graph, p is the y ordinate and V the x ordinate. So the integral is equivalent to $\int y.dx$. what's a geometric interpretation of that integral?

7. Jan 8, 2016

### kent davidge

oh yes, I see that and I solve the problem by this way. But I wonder if there's anyway to solve this integral for T using only calculations without the graph. Is there a way?

8. Jan 8, 2016

### haruspex

Yes, but you first have to turn the graph into an equation relating p to V. Then plug that function into $\int p.dV$.

Edit: When you say you solved the problem that way, are you referring to your solution in post #3? That solution was wrong.

9. Jan 8, 2016

### kent davidge

Ok. Thank you.

10. Jan 8, 2016

### Mister T

They do not want an answer with a ± sign in front of it. They want a positive number and they want you to determine whether it's "on" or "by".