Thermodynamics: cylindrical figures contains a gas

[mtayab1994]

Homework Statement

A cylindrical figures contains a gas and we have a piston that is capable of changing the gases volume.
Initial state: V0=1l P0=10^5p T=300°K

We pressurize on the piston that has a mass m=300g and a surface S=20cm^2.
The new temperature T1=540°K

Homework Equations

Calculate the change in internal energy.

The Attempt at a Solution

Well I know that the change in internal energy is: ΔU=W+Q or ΔU=-P1(V1-V0)

and that p=F/S. but since my teacher didn't explain the lesson well enough I have no clue on how to answer it. Any help would be very well appreciated.

 

[Simon Bridge]

Can you draw the p-V diagram?

You have a state equation for the gas.
You have the initial state.
You have two values for the final state.
Which means you know the final state.

Which internal energy equation is valid for this system?

Note:
http://en.wikipedia.org/wiki/Internal_energy#Internal_energy_changes

 

[mtayab1994]

i believe i would have to use this one right?

I would get: ΔU=p1(V0-V2)+Q right?

 

[Simon Bridge]

OK, I'll let you off the hook:
Internal energy for an ideal gas depends only on it's temperature.
$$\Delta U = \frac{3}{2}nR\Delta T$$

You know the change in temperature - it's given to you.
You need to find nR.

 

[mtayab1994]

OK, I'll let you off the hook:
Internal energy for an ideal gas depends only on it's temperature.
$$\Delta U = \frac{3}{2}nR\Delta T$$

You know the change in temperature - it's given to you.
You need to find nR.

alright i'll give it a try right now.

 

[mtayab1994]

I got n=.0401 by using the equation of ideal gases and i got a change of internal energy as 55J correct?

 

[mtayab1994]

I got n=.0401 by using the equation of ideal gases and i got a change of internal energy as 24.5J.

Is this correct?

 

[Simon Bridge]

I've not done the math so I cannot tell you.
But it's numbers-in-numbers-out, hard to go wrong.