Acarnot engine is operated between two heat reservoirs at temperatures of 520 k and 300 k. (a) if the engine receives 6.45 kj of heat energy from the reservoir at 520 k in each cycle, how many joules per cycle does it discard to the reservoir at 300 k? (b) how much mechanical work is performed by the engine during each cycle? (c) what is the thermal efficiency of the engine? 20.13 . a