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Work done in Adiabatic, Quasistatic-compression

  • Thread starter Trenthan
  • Start date
  • #1
54
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Homework Statement


i have to find the W done in an Adiabatic, Quasistatic compression and im not having much luck.

Ive calculated it using (delta)U = Q + W, since Q = 0, hence W = change in internal energy

However i want to calculate it using W = -(delta)P*V

The Attempt at a Solution



My working is attached, my text just says to use W = delta(U), but i know there is a way to do it via pressure and volume, im just not sure where to go from where im at.

Attempt is attached

Untitled-Scanned-03.jpg


Has to be in terms of TA, n (moles) and R

Cheers Trent
 

Answers and Replies

  • #2
162
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I assume we are talking about perfect gases so that indeed [tex]p V^\gamma = const [/tex] for a quasistatic, adiabatic process :p

[tex]

-\int_{V_C}^{V_A} p dV =

\left\{ p V^\gamma = const \right\}=

-\int_{V_C}^{V_A} const \cdot \frac{dV}{V^\gamma}

[/tex]

Determine [tex] const [/tex] from the conditions at A.
 
  • #3
54
0
I assume we are talking about perfect gases so that indeed [tex]p V^\gamma = const [/tex] for a quasistatic, adiabatic process :p

[tex]

-\int_{V_C}^{V_A} p dV =

\left\{ p V^\gamma = const \right\}=

-\int_{V_C}^{V_A} const \cdot \frac{dV}{V^\gamma}

[/tex]

Determine [tex] const [/tex] from the conditions at A.
I got it finally thanks heeps but i got it using conditions at "c" our starting point, (PCVCgamma = PVgamma, rearranged for P = and solved from ther) not "A", im assuming u meant "c"???

Thanks :)
 
  • #4
162
0
Oopsie, yes I meant "C" , it's the point where you know P and V to start with. Sorry, I always think that A comes before C when I'm not thinking :P:P

Though now that you said, . . . it's also true that you know P and V of point A too, so you could use any:) of course, they've given you two points such that :
[tex]


p V^\gamma = const1


[/tex]
and
[tex]


T V^{\gamma-1}= const2


[/tex]
with
[tex]


\gamma=5/2


[/tex]
because if this was not so it wouldn't be a reversible, adiabatic process.
 
  • #5
54
0
thanks and good point, just trierd it the other way and it works :)
 

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