A Carnot engine takes 3000 J from a reservoir at 600 K does some work and discards some heat to a reservoir at 300 K. What is its efficiency?

The efficiency of a Carnot engine is given by the formula: Efficiency = 1 - (Tc/Th), where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir. Plugging in the values (Tc = 300 K, Th = 600 K), we get an efficiency of 50%.