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Quiz3_Physics241_S09

# Quiz3_Physics241_S09 - £ = J-= l_l 2 73-f-5 = o ·as(27.3...

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/(e y Quiz 3- 16 February 2009 Name: ----+------- Recitation Day/Time _ 1. Find the change in entropy when 3.0kg block of copper is slowly cooled from 350.0 o C to 50.0 o C. (C cu = 386Jlkg.K) (4 point) () = I'l7C t1 T I d { = frJC LJ S = f _tf -:= f h·y ciT /rz (2.7~-t50) (:2737"65 0 ) T " T = 3·0 k:J x 311 bJI~ -k.. X -0-66 fjS =- -7bO J; J::. l' 2. A heat engine operates between a hot reservoir at T H = 225°C and a cold reservoir at T L = 50°C. It uses 300J of heat per cycle taken from the hot reservoir while doing 80J of work. a) Find the theoretical efficiency of an ideal engine operating between these two temperatures. b) What is the actual efficiency of the heat engine? c) The How much heat is exhausted per cycle to the cold reservoir? (3 points) Iclef1/
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Unformatted text preview: £ = J-= l_l 2 73-f-5 ) = o ·as (27.3 t 2.'25 ) ~) ReV1/ £ c=: U~ ~ 80J = .2{,b 2(;.6(-(erN J .3 00 J e) 1--1 e a f { Z It Ct U ~ /-e c( = fie tL f C1 d Jut -ki 0 r-L c/.L; I1J-= 300 I -6v"J" = :2'-J . 3. A quantity of2.25 moles of ideal monatomic gas (Cy = 3R12) is slowly cooled at constant pressure from 350.0 o C to 125.0 o C. Find the net change in entropy of the gas. (3points) Ll s ~ S ~ 4' ~ t'1. f C f d T ~ he In / (' / T . f T; -7 _ IJ.J .. ~3-t-J!. .'5) . =-A-J-5 x J x g. '.:11 ). (:273 -r a 50) = 2.;25 x2 x g-3i ~-O'4ft. :2-tJ S-;20 . 1 5 T / k. t llE = Q-W Q = mc.1lT G = 1_ IQL1 = IQHI Q=mL M = fdQ/T 1 _ T L T H PV=nRT itlE = nCy.1lT =J!.1 fQHI C p = Cy+R Q = nC.1lT W = fPdV Qy = nCyllT R = 8.31 J/mol.K=...
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