Question

Air having a pressure of 40 psig and a volume of 8 cu ft expands isothermally to a pressure of 10 psig. Find the external work performed during the expansion.

Answer 1

Answer:

357.6 lb-ft

Explanation:

V = Volume = 8 ft³

dP = Change in pressure = (40-10) = 30 psig

Work done is given by

$W=VdP\\\Rightarrow W=8\times (40-10)\\\Rightarrow W=240\ psig.ft^3$

$30\ psig=44.7\ psi\\\Rightarrow 1\ psi=\dfrac{30}{44.7}$

So, converting to ft-lb

$\dfrac{240}{\dfrac{30}{44.7}}=357.6\ lb-ft$

The external work performed during the expansion is 357.6 lb-ft