Physics Exercises/Heat Engines

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  1. At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. The operating temperatures of the first are 800 deg C, and 500 deg C, and of the second 485 deg C and 300 deg C. If the heat of combustion of coal is 2.8 x 107 J/kg, at what rate must coal be burned if the plant is to put out 1 GW of power? Assume the efficiency of engines is 70 percent of the Carnot efficiency operating between the said temperatures.