# Physics difficult... chris help again plz.

A heat engine has the three step cycle shown above. Starting from point A, 1 L (liter) of ideal gas expands in the isobaric (constant pressure) process A to B at P = 2 atm. B to C is isovolumetric process at V = 5 L, and C to A is an isothermal (constant temperature) compression at 300 K. (Note that the diagram is illustrating V vs P. This should make no difference in your calculations. )

i found the pressure at point C to be .4 atm and the heat exhausted from B to C to be 6000J

also on the picture it shows from C to A T=300[k]

If the net work done by the engine per cycle is 480 J, find the work done by the gas during process C to A??.

i got -5681 but that isn't right

* Physics - Chris, Friday, May 7, 2010 at 8:29pm

pA = pB = 2 atm = 2 * 101325 Pa = 202650 Pa
vA = 1 L = 1 * 10^-3 m^3
vB = 5 L = 5 * 10^-3 m^3
W(A to B) = 202650 * (5 * 10^-3 - 1 * 10^-3) = 202650 * 4 * 10^-3 = 810.6 J
W(B to C) = 0 (because volume is constant)
W(in complete cycle) = 480 J

W(in complete cycle) = W(A to B) + W(B to C) + W(C to A)
480 = 810.6 + 0 + W(C to A)
W(C to A) = 480 - 810.6 = -330.6 J
Ans: -330.6 J

That isn't the right answer either.

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