A power cycle operates between two reservoirs having temperature 700 K and 300K, respectively. QH is the heat (thermal energy) received from the hot reservoir. QL is the heatrejected to the cool reservoir. Wmech represents the mechanical work produced. Please determineif the following cycles are possible and explain why?
(A). QH=700 kJ, Wmech=400 kJ, QL=300 kJ;(B). QH=700 kJ, Wmech=500 kJ, QL=200 kJ;(C). QH=700 kJ, Wmech=300 kJ, QL=600 kJ;(D). QH=700 kJ, Wmech=600 kJ, QL=100 kJ;

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.