An alert physics student stands beside the tracks as a train rolls slowly past. He notes that the frequency of the train whistle is 459 Hz when the train is approaching him and 445 Hz when the train is receding from him. Using these frequencies, he calculates the speed of the train. What value does he find

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If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.

Ibelieve the answer is d. densityhope my answer has you : )