Question

A gas contained in a vertical piston–cylinder assembly by a
piston with a face area of 40 in^{2} and weight of 100
lb_{f}. The atmosphere exerts a pressure of 14.7
lb_{f}/in^{2} 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 4 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.

Answer #1

A gas undergoes a process in a piston–cylinder assembly during
which the pressure-specific volume relation is
pv1.2 = constant. The mass of the gas
is 0.4 lb and the following data are known: p1
= 160 lbf/in.2, V1 = 1
ft3, and p2 = 300
lbf/in.2 During the process, heat transfer from
the gas is 2.1 Btu. Kinetic and potential energy effects are
negligible. Determine the change in specific internal energy of the
gas, in Btu/lb.
Δu=

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