An inventor claims to have developed a power cycle having a thermal efficiency of 40%, while operating between hot and cold reservoirs at temperature th and tc 5 300 k, respectively, where th is (a) 900 k, (b) 500 k, (c) 375 k. evaluate the claim for each case

From Carnot's theorem, for any engine working between these two temperatures:

efficiency <= (1-tc/th) * 100

Given: tc = 300k (from question assuming it is not 5300 as it seems)

For a, th = 900k, efficiency = (1-300/900) = 70%

For b, th = 500k, efficiency = (1-300/500) = 40% 

For c, th = 375k, efficiency = (1-300/375) = 20% 

Hence in case of a and b, efficiency claimed is lesser than efficiency calculated, which is valid case and in case of c, however efficiency claimed is greater which is invalid. 

i believe it is b. what was the cause of the big bang

hope this !