A combined device consists of two machines operating simultaneously: • Machine A…
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Thermodynamics · Thermodynamics
Problem
A combined device consists of two machines operating simultaneously:
• Machine A absorbs 400 J of heat from a reservoir at 550 K, rejects 300 J of heat to a reservoir at 350 K, and delivers 100 J of mechanical work.
• Machine B uses the 100 J of work from Machine A to remove 400 J of heat from the 350 K reservoir and deliver 500 J of heat to the 550 K reservoir.
For one simultaneous cycle of the combined device, which statement is most accurate?
(a) The combined device is permissible because the entropy gained by the 550K reservoir exactly cancels the entropy lost by the 350K reservoir.
(b) The combined device is impossible because the total entropy change is positive.
(c) The combined device is impossible because the total entropy change is negative.
(d) The combined device is impossible because it violates the first law of thermodynamics; the energy transfers at 550K do not balance.