Air pressure in cylinder?

1. Apr 2, 2009

83bob83

1. The problem statement, all variables and given/known data
in a cylinder there is 30g of air which starts with a volume of 3L and pressure 0.1MPa. What will be the density of the air when the piston of the cylinder compresses the air to 0.5MPa ?

2. Relevant equations

3. The attempt at a solution

2. Apr 2, 2009

fluidistic

Where are you stuck?
PV=nRT, density=mass/volume.

3. Apr 2, 2009

83bob83

I don't know where to start

4. Apr 2, 2009

fluidistic

I'm not really sure, but if we suppose the temperature don't change then the problem is easy.
You are told that the pressure increases by a factor 5. So what can you say about the volume?
Use the formulas I gave you. (are you familiar with them?)

5. Apr 2, 2009

83bob83

yes the temperature stays constant. the volume will decrease so the density will increase? I'm not sure how to use the formulas what does each variable stand for?

6. Apr 2, 2009