A piston-cylinder apparatus has an initial volume of 1.00 ft3. a) The apparatus is filled with air at 100 lbf/in2 gage and 68°F. The piston is moved outward until the pressure is atmospheric, 14.7 lbf/in2 absolute. Assuming that temperature remains constant and that the air behaves as an ideal gas, what is the final volume? What is the work done by the air on the piston? Answer: 7.80 ft3, 33900 ft-lbf b) The apparatus is filled with water at 100 lbf/in2 gage and 68°F. The piston is moved outward until the pressure is atmospheric, 14.7 lbf/in2 absolute. Assuming that temperature remains constant and that the water behaves as an incompressible liquid, what is the final volume? What is the work done by the water on the piston? c) For safety reasons, pressure vessels are usually tested with water pressure rather than with air pressure. How do you explain this in terms of the answers to (a) and (b)?