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Calculation actual efficiency problem

  • Thread starter astru025
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1. 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?

2. 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.

3. The Attempt at a Solution

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

CWatters

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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?
 
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445 j?
 

CWatters

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So if 1030J goes in and only 445J comes out in the form of useful work the efficiency is ?
 
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445 J / 1030 J = 43 % thanks very much!
 

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