How to Calculate Efficiency and Heat Rejection in an Engine?

AI Thread Summary
To calculate the efficiency of an engine, divide the work done (120J) by the energy absorbed (400J), resulting in an efficiency of 30%. The heat rejected in each cycle can be determined by subtracting the work done from the energy absorbed, yielding 280J. The discussion emphasizes the application of the first law of thermodynamics, which states that the net energy change in a closed system is zero after a complete cycle. Participants seek clarification on these calculations, confirming the methods used. Overall, the thread provides a straightforward approach to understanding engine efficiency and heat rejection.
jin
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heat system efficiency??

So lost..so what am i suppose to do??

'An engine absorbs 400J of heat and does 120J of work in each cycle'

a)what is its efficiency?
b)how much heat is rejected in each cycle?
 
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For a cycle, that is, when after a process, a system comes back to its original state, the difference of the net energy taken and work done by it is zero - first law of thermodynamics.

Efficiency = \frac{work done}{energy taken}


spacetime
www.geocities.com/physics_all/index.html
 
so...i just go 120/400 x 100?

how do i calculate th heat rejected in the cycle?? the left over? 400-120??
 
correct!

spacetime
 
thanks! can u help me with the others on another post?? please ><
 

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