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Unformatted text preview: Kegﬁ
Name: Student lD#: Physics 344 — Midterm 2
March 16, 2009 1. An object at 30°C is in thermal contact with a heat reservoir whose temperature is
80°C, the temperature of the object eventually reaches 80°C. The heat capacity of the object is constant, C=1OO :J/K. _ 8666 2 35.3. [r K
a. Find the change In entropy of the object.
b. Find the change in entropy of the reservoir. 3 o“( : Z03. INC 0. Consider the object and the reservoir as a composite isolated system, what is
the change in total entropy? Should it be zero? Why (or why not)? 1:
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an i‘irvvrréré/e adiabniic prams, Agni”) . 2. Two objects, A and B, of identical mass and composition, have initial temperatures
500K and 300K, respectively. The heat capacity of A, as well as B, is 200 J/K. The two objects form an adiabaticaliy enclosed system. What is the maximum output work can
be performed by the system? mAce
A = ———'— =1:
5. T,
if
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TIC
(‘x = C. ' 6“ W,’ Oz kj‘ (Qt "Q7, .—
.— 3. A turbine receives 300 kg/s saturated water vapour at 50°C and rejects the flow as
saturated liquid water at 50°C. The environment temperature is 20°C. a. Calculate the change in specific entropy between the exit and entry states of
water. b. Calculate the specific exergy. What does it tell you? 9790'" 50°C a l, trfula’ S‘oC 50°C = 3234!” K
W, 20% 7273.1; K As: gba SQ 2048.! = ~74 £34.56” (7). M 7:272.1t/<7 40:2.“4/73/‘3’ 50:3.7éj/Kﬁ2 ‘2 as
0
M £0 __ 7;§° _ Z‘ﬂ‘X/o _z73‘/$—x8.7 X/o :A/O 2
b 2 a a was“ 2257 ‘ 17:. WWW 1%
a: b—bé‘: 120" (“°) = 2}!) MM out?“ WW" " ganxe :6? MW 5370 MW.
oil; e =6ﬁaTm1’5 all: e 2 (T‘~Tm)($a’5b) 4. The energy representation of the fundamental relation of a photon gas (black body
radiation) can be expressed as U(S, V) = aV1/384/3 where a is a positive constant. a. Determine the entropy S(V, T).
b. Determine the enthalpy H(S, V). 0). ms, V) = a V‘J/‘gt/Z’ w: 75/5 — 7241/ .__aol ~ 4/; V;
(’(Egv‘éﬁav S
93; M3
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b Til/L ...
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 Spring '09
 MichaelChen
 Physics

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