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falsealarm715

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## Homework Statement

Two pounds of air contained in a cylinder expand without friction against a piston. The pressure on the back side of the piston is constant at 200 psia. The air initially occupies a volume of 0.5 ft

^{3}. What is the work done by the air in ft-lbf if the expansion continues until the temperature of the air reaches 100 F?

## Homework Equations

Q - W = m(u

_{f}- u

_{i}), which translates to W = m*c

_{v}*(T

_{f}- T

_{i}) [Q is 0 because there's no heat transfer]

PV = mRT

## The Attempt at a Solution

W = 2 lbm (0.171 Btu/lbm R)(559.67 R - T

_{i})

The text says the answer is 45300 ft-lbf

Basically I don't really know how to start this all off. I know I need to find the initial temperature which I think means I need to use PV = mRT but I can't find an agreeable R value in my book (also I have no idea if my c

_{v}value is correct). Could someone just point me in the right direction?

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