Answer:
3.48) Work done by the air is 1.05 kJ
3.54) 4.12 kJ of work is given out
Explanation:
3.48) Work done (W) = P2V2 - P1V1
P1 is initial pressure of air = 150 kPa
V1 is initial volume of air = 1 L = 1/1000 = 0.001 m^3
P2 is final pressure of air = 800 kPa
V2 is final volume of air = 1.5 L = 1.5/1000 = 0.0015 m^3
W = (800×0.0015) - (150×0.001) = 1.2 - 0.15 = 1.05 kJ
3.54) For a polytropic process
W = (P1V1 - P2V2)/(n - 1)
P1 is initial pressure of helium = 125 kPa
V1 is initial volume of helium = 0.25 m^3
P2 is final pressure of helium = 100 kPa
n is polytropic exponent = 1.667
V2 is final volume of helium = V1(P1/P2)^(1/n) = 0.25(125/100)^(1/1.667) = 0.25(1.25)^0.5999 = 0.25(1.14) = 0.285 m^3
W = (125×0.25 - 100×0.285)/(1.667 - 1) = (31.25 - 28.5)/0.667 = 2.75/0.667 = 4.12 kJ
