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Unformatted text preview: Physics 613
Discussion Section Extrn~Credit Problem #6 (This is a kind of long tine — do as much as you can, but try not to get bogged down in calculations;
you can do them all in your head.) Useful Equations:
A U .-.— sQ --- w é *3 __.
ASS-“(2" assurances-Is” O T You are minding your-own business when two inventors rush up to you, both excited to descrribe the new
heat engines they have designed. Inventor A tells you that during each cycle that his engine turns through, it takes 1000 Joules of heat from a .
furnace at temperature 227 Celsuis, dumps 300 Joules of heat into a cold exhaust reservoir at temperature 2? Celsuis, and does 700 Joules of useful owrk. Inventor B tells you that her engine, during each cycle, also takes 1000 Joules of heat from the same 227-
Celsuis furnace. It sumps 900 Joules of heat into the cold ZT—Celsius reservoir, and does 300 Joules of useful work. Both engines end each cycle in exactly the same internal state that they started in. a) For each inventor — A and B — calculate the change in entropy of the hot furnace during one cycle of hte
engine. ' .r‘l b) For each inventor — A and B —
cycle of hte engine. c) For each inventor _ A and B — what is the change in entropy of the engine itself during one cycle of the
engine? (Remember that the engine ends the cycle in exactly the same state that it started!) d) Do you believe that inventor-A’s engine actually works? Why or why not? e) Do you believe that inventor his engine actually works? Why or vvhj,I not? f) So you invent your own engine, which also takes 1000 J of heat from the 227:Celsius hol reservoir
during each cycle, and dumps some exhaust heat into the colder ZZ—Celsius reservoir.. What is the greatest possible useful vvork that your engine might be able to do during each cycle?r ...
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- Winter '08