What is the Thermal Efficiency of an Engine?

AI Thread Summary
The discussion focuses on calculating the thermal efficiency of an engine using the equation e=(Qh-Qc)/Qh. Participants emphasize the importance of understanding the three thermodynamic processes: isobaric, isochoric, and adiabatic, and how they relate to the variables of pressure, volume, and temperature. There is a call for more information to solve the problem effectively, as the provided graph lacks sufficient data. Users are encouraged to attempt the problem independently and share their work for further guidance. The conversation highlights the need for a clear understanding of thermodynamic principles to derive the correct solution.
yecko
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Homework Statement


http://i.imgur.com/SQ6jx94.png
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
 
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Show your working.

yecko said:
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.
 
CWatters said:
what is constant during an isobaric, isochoric, or adiabatic process.
isobaric=>p constant
isochoric=>v constant
adiabatic=>q constant
 
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?
 
yecko said:
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.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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