What is the Thermal Efficiency of an Engine?

[yecko]

Homework Statement

http://i.imgur.com/SQ6jx94.png

(sorry for the low resolution~ it's already the best i can make it~)

Homework Equations

U=Q+W
the three variables of isobaric, isochoric, adiabatic process (can i save my effort from typing all of them out?)
e=(Qh-Qc)/Qh

The Attempt at a Solution

Substitute the relevant equations in order to get Qc & Qh
it always seems a lack of information to the three points
there should be a specific route for substituting the variables to the cycle and the few thought by me should be wrong
can anyone tell me the right way to get option "e" here?

Thank you

 

[CWatters]

Show your working.

it always seems a lack of information to the three points

I haven't attempted a solution but usually these come from the data provided on the graph combined with your knowledge about what is constant during an isobaric, isochoric, or adiabatic process.

 

[yecko]

what is constant during an isobaric, isochoric, or adiabatic process.

isobaric=>p constant
isochoric=>v constant
adiabatic=>q constant

 

[CWatters]

So of P, V, and T which are you missing at each of the three points and how might you work them out from the info provided?

 

[Elvis 123456789]

isobaric=>p constant
isochoric=>v constant
adiabatic=>q constant

You must attempt the question yourself. Get as far as you can and then post that attempt here so that the homework helpers can see where your misunderstanding comes in.

 

[yecko]

http://imgur.com/kU72GXT
Heres my rough work if you don't mind they are a little bit untidy
Thanks