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chuffy
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Homework Statement
1kg of helium in a closed system has 40kj added by heating & 100kj removed by work during a reversible polytropic process.
The initial temp of the gas is 300K & the initial pressure is 100kN/m2
Q. find the final temp of the gas & pressure
Homework Equations
given: Cp=14.57 kgK & M=4
The Attempt at a Solution
Hi guys, I can't get my head around how to work out the final pressure (P2)
I got the Temp correct (T2) bu doing the following:
R=Ru/M
R =2.0785
Cv = R +Cp
Cv = 7.2715
closed system so V= const
Qnet = -100 -40 =-140
qnet = Q/m
qnet = Cv(T2-T1)
T2 = 281K
Can't think how to work out P2 when I don't have n
any help?