How Much Energy is Needed to Heat Air in a Movable Piston Cylinder to 755 K?

[lackos]

Homework Statement

A vertical cylinder with a heavy piston contains air at 315 K. The initial pressure is 2.85 105 Pa, and the initial volume is 0.250 m3. Take the molar mass of air as 28.9 g/mol and assume CV = 5/2R.

(d) Assume again the conditions of the initial state and assume the heavy piston is free to move. Find the energy input required to raise the temperature to 755 K.
4 kJ

Homework Equations

Q=nCp(delta)T;
and possibly;
(delta)E=Q+W

The Attempt at a Solution

im confused as to whether all i need to use is the first equation or if in need to factor in the work done.
i already have to number of moles and Cp=7/2R
Thanks!

 

[method_man]

I would say that you also need to calculate the work done. Because the piston is "free to move". If the piston has moved, there has been a change in the volume. If there is a change in the volume, there is work done.