# Calculation actual efficiency problem

#### astru025

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!

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#### CWatters

Homework Helper
Gold Member
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?

445 j?

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Gold Member
2018 Award

#### CWatters

Homework Helper
Gold Member
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!

"Calculation actual efficiency problem"

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