# Cylinder gas, pressure question

http://img15.imageshack.us/img15/9746/21478397.png [Broken]

I know how to setup the entire problem i just dont know how to calculate the new pressure after the piston is compressed.

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LowlyPion
Homework Helper
I know how to setup the entire problem i just dont know how to calculate the new pressure after the piston is compressed.
PV = nRT

n, R, T remain the same. They give you everything else.

PV = nRT

n, R, T remain the same. They give you everything else.
how do i calculate the number of moles?

maybe p1v1/t1 = p2v2/t2 is more appropriate?

maybe p1v1/t1 = p2v2/t2 is more appropriate?
i dont think so, this is actually from my physics class and we never covered that

ok fair enough
just out of interest is the answer 234375 Pa?

mgb_phys
Homework Helper
What Rory is saying is that PV = nRT is the general equation but nRT and are constant
So p1v1 = p2v2, rearrange a little and you have the answer

ok fair enough
just out of interest is the answer 234375 Pa?
not sure, has yet to be handed in

ahhh yes even more simple! forgot the temperature remained constant!
ok fair enough, would you be as kind enough to tell us the answer as i am revising for my physics A-level at the minute so all questions are useful!!!

mgb_phys
Homework Helper
just out of interest is the answer 234375 Pa?
No.

The volume goes from 0.750 -> 0.480 m^3, the pressure starts at 1.50 x10^5 Pa
so the final pressure is (0.750/0.480) * 1.50 x10^5 Pa = 2.34 x10^5 pa

No.

The volume goes from 0.750 -> 0.480 m^3, the pressure starts at 1.50 x10^5 Pa
so the final pressure is (0.750/0.480) * 1.50 x10^5 Pa = 2.34 x10^5 pa

lol thats the answer i got, except yours is in standard form! lol

mgb_phys
Homework Helper
This is a 'physics' A level not maths
2.34 x10^5 is correct 234375.000000000000000000000 pa is wrong - whatever your calculator says!

Hint, whats the precision of the initial pressure measurment

oooohhh slightly harsh!!
but never the less thats fair enough!
no wonder my physics teacher is always annoyed with me for leaving whole answers!!!

maybe p1v1/t1 = p2v2/t2 is more appropriate?
yea this is the correct way to do it, thanks

ahhh yes even more simple! forgot the temperature remained constant!
ok fair enough, would you be as kind enough to tell us the answer as i am revising for my physics A-level at the minute so all questions are useful!!!
http://wug.physics.uiuc.edu/cc/IAState/Phys221/spring/homework/written%20homework/index.html [Broken]

have at it.

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