How Does Compression Affect Air Density in a Cylinder?

[83bob83]

Homework Statement

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 ?

Homework Equations

The Attempt at a Solution

 

[fluidistic]

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

 

[83bob83]

I don't know where to start

 

[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?)

 

[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?

 

[fluidistic]

Yes, the density will increase as the volume decreases.
I suggest you to read http://en.wikipedia.org/wiki/Ideal_gas_law to see in details what the variables in PV=nRT stand for.