# PV^n=constant (refresher)

1. Sep 14, 2008

### Saladsamurai

1. The problem statement, all variables and given/known data
A closed system consisting of 2 lb of a gas undergoes a process in which pV^n=constant. For: p1=20 lb/in^2 , V1=10 ft^3 and p2=100lb/in^2 V2=2.9 ft^3

(a)What is n ?

(b)What is the specific volume at states 1 and 2 in ft^3/lb?

(c)Sketch the process on pressure-volume coordinates

For (a), I don't need to convert the units all to feet or all to inches right? i can just say p1V1^n=p2V2^n correct?

(b) Is just a matter of find the mass m=Weight/g

(c) Is confusing me? Is this just a graph? With p on the horizontal axis and V on the vertical?

Thanks!!!

2. Sep 14, 2008

### Saladsamurai

Okay, I got (a).....the units cancel anyway.

But for (b) I cannot tell if they are giving me 2lb as a mass or as a weight. It's a thermodynamics book, so I don't know what the convention is? they did not specify lbf (force) or lbm (mass)

3. Sep 15, 2008

### Andrew Mason

Correct.

$$P_1V_1^n = 5P_1(.29V_1)^n$$

Correct

You have to plot points in between the end points as well.

AM

4. Sep 15, 2008

### Andrew Mason

Are the units of pressure Force/area or mass/area?

AM

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