A system undergoes a two-step process as sketched in the figure below. The syste

Question

A system undergoes a two-step process as sketched in the figure below. The system first expands at constant pressure from state i to state A and then it is compressed with the pressure again held fixed, ending with the system in state f. What is the approximate amount of work done by the system during each step? (Assume V1 = 0.4 m3 and V2 = 0.8 m3.)

Estimate the pressure of the system.
Pa

Estimate the volume at state i.
m3

Estimate the volume at state A.
m3

Estimate the volume at state f.
m3

Calculate the work done by the system during the expansion step. (Use your estimates.)
J

Calculate the work done by the system during the compression step. (Use your estimates.)
J

Explanation / Answer

a) Because the pressure is relatively the same throughout the system you can assume it to be constant at 15,000 Pa

b) Volume at state i = .2 m3

c) Volume at state A = .9 m3

d) Volume at state f = .4 m3

e) If pressure stays constant you can use the equation W=P(V2-V1). So from that you get W=15,000(.9-.2) = 10500J

f) Same equation W=P(V2-V1). W=15,000(.4-.9) = -7500J

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