A piston-cylinder contains air at a pressure of 500 kPa. The piston movement is resisted by a spring and atmospheric pressure of 100 kPa. The air moves the piston and the volume changes from 0.15 m3 to 0.60 m3. Determine the work when
(a) the force of the spring is directly proportional to the displacement;
(b) the force of the spring is proportional to the square root of the displacement;