A gas is inside a cylinder closed by a piston. The piston is held from above by a spring whose elastic properties obey Hooke's law. Produce a rough sketch, in the `p V-` coordinates, of the curve that represents the change in state of the gas upon heating and determine the work that is done in the process if the volume of the gas varies from `v_1` to `v_2` and the pressure varies from `p_1` to `p_2`.