Agas is contained in a vertical piston–cylinder assembly by a piston with a face area of 60 in2 and weight of 100 lbf. the atmosphere exerts a pressure of 14.7 lbf/in2 on top of the piston. a paddle wheel transfers 3 btu of energy to the gas during a process in which the elevation of the piston increases slowly by 3 ft. the piston and cylinder are poor thermal conductors, and friction between the piston and cylinder can be neglected. determine the change in internal energy of the gas, in btu.