5.9 An ideal gas contained in a well-insulated piston-cylinder device is at equilibrium with the surrounding atmosphere. The piston is first pushed to compress the gas from its initial volume

(V) to final volume (V,). The piston is then released and the gas allowed to expand until it reaches equilibrium. Draw the process on a P-V diagram assuming (a) that the piston is frictionless and (b) that the piston has friction.