3. An aircraft engine takes in 9000 J of heat and discards 6400 J of heat each cycle. (a) What is the mechanical work output of the engine during one cycle? (b) What is the thermal efficiency of the engine? 4. Two objects, B,(T=40.C) and B2(T=18.C), experienced entropy changes of 6.4 x 10* J/K and 2.8 x 104 K, respectively after they had been placed in direct contact with each other. B, lost 2.0 x 10' J of heat. How much heat was lost by B2? What was the entropy change in the universe after the process? Z