A heat engine operating between 100°C and 700°C has efficiency equal to 40% of the maximum theoretical efficiency .how much energy does this engine extract from the hot reservoir in order to do 5000J of mechanical work?

Answer 1

100 + 273 = 373 deg K
700 + 273 = 973 deg K
ideal Carnot eff = 1 - Tl/Th = 1 - 373/973 = 0.6166
real efficiency = 0.40* .6166 = 0.2467
so 5000 J / 0.2467 = 20,268 Joules