Calculation actual efficiency problem

[astru025]

Homework Statement

A heat engine takes in 1030 J of energy at 1000 K and exhausts 585 J at 250 K. What are the actual and maximum theoretical efficiencies of this heat engine?

Homework Equations

For maximum efficiency I got 75 % by taking 1 - (250K / 1000K). For actual efficiency the equation is W/ Q or work out / heat in.

The Attempt at a Solution

I am not sure where to start on this problem and any help would be very nice!

 

[CWatters]

The max efficiency is the Carnot efficiency which you seem to have right (I think).

As for the actual efficiency...

For actual efficiency the equation is W/ Q or work out / heat in.

Correct.

If 1030 J goes into the engine and 585J comes out of the exhaust how much is used elsewhere by the engine, presumably doing useful work?

 

[astru025]

445 j?

 

[haruspex]

445 j?

Yes.

 

[CWatters]

So if 1030J goes in and only 445J comes out in the form of useful work the efficiency is ?

 

[astru025]

445 J / 1030 J = 43 % thanks very much!