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## Homework Statement

18. (II) At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate ehat input of the second. Th eoperating temeprautres of the first are 680 degrees C and 430 degrees C, and of the second 415 degrees C and 280 degrees C. If the heat of combuston of coal is 2.8 E8 J/kg, at what rate msut coal be burned if the plant is to put out 900 MW of power. Assume the efficiency of the engines is 65 percent of the ideal (Carnot) efficiency.

## Homework Equations

e = |W|/|QH|

were the H is the subscript

e ideal = 1-TL/TH

were L and H are subscripts

## The Attempt at a Solution

Ok I calculated the efficiency of the first engine to be about 17.05 % efficient and the second one to be about 14.64 % efficient.

I know that efficiency is

e = |W|/|QH|

were the H is the subscript

I know that 900 MW is a value of power which is not work

I know that |QH| is 2.8 E8 J/kg but I do not like the units for this, J/kg, as I thought Q was measured in joules only...

How do I find the work done?