647_Physics ProblemsTechnical Physics

647_Physics - Chapter 22 P22.42 649 c iron = 448 J kg C c water = 4 186 J kg C b gd ib gb gd Qcold = Q hot 4.00 kg 4 186 J kg C T f 10.0 C = 1.00

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Chapter 22 649 P22.42 c iron ±Jkg C =⋅ ° 448 ; c water Jkg C ° 4186 QQ cold hot =− : 400 100 448 900 .. . kg 4 186 J kg C C kg J kg C C ⋅° ° = − ⋅° ° bg di b g TT ff which yields T f = 33 2 306 2 C K S cmd T T T T Sc m c m S S =+ = F H G I K J + F H G I K J + ⋅− = zz water water K 306.2 K iron iron K 306.2 K water water iron iron J kg K kg J kg K kg JK 283 1173 306 2 283 306 2 4 00 0 078 8 448 1 00 1 34 718 ln . ln . . . b g b g b g b g af P22.43 Sitting here writing, I convert chemical energy, in ordered molecules in food, into internal energy that leaves my body by heat into the room-temperature surroundings. My rate of energy output is equal to my metabolic rate, 2500 2500 10 120 3 kcal d cal 86 400 s J 1 cal W = × F H G I K J = . . My body is in steady state, changing little in entropy, as the environment increases in entropy at the rate ∆∆ S t QT t Qt T == = = 120 04 1 W 293 K WK .~ . When using powerful appliances or an automobile, my personal contribution to entropy production is much greater than the above estimate, based only on metabolism.
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .

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