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Physics Final

# Physics Final - LBS 271 Final Fall 2003 There is supposed...

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LBS 271 - Final Fall 2003 Page 1 of 6 There is supposed to be only one correct answer per question. If you can’t find one, choose the one closest to your answer. Problem 1 How much heat is needed to take 5 kg of ice at –40 °C to water vapor at 140 °C? c ice = 0.53 kcal/°C·kg, L fusion = 80 kcal/kg c vapor = 0.48 kcal/°C·kg, L vaporization = 540 kcal/kg a) 3800 kcal b) 1100 kcal c) 0.17 kcal d) 3.0·10 9 e) 100 kcal Problem 2 Two rods are made of the same material, but Rod A is 4.0 mm in diameter and 4.0 m long, and Rod B is 2.0 mm in diameter and 8.0 m long. What should be the ratio of the temperature changes Δ T A / Δ T B so that both rods would expand the same amount (same Δ L) ? Problem 3 In the pV diagram shown a gas undergoes a complete cycle. How much work is done by the system? Problem 4 An inventor claims that his engine takes in 1000 J of heat and exhausts only 100 J at 27 °C. If this is true, what must be the minimum temperature of the heat source? Problem 5 A metal wire is in thermal contact with two heat reservoirs at both of its ends. Reservoir 1 is at a temperature of 769 K, and reservoir 2 is at a temperature of 331 K. Compute the total change in entropy (J/K) arising from the conduction of 1410 J of heat through the wire. a) 1.07 b) -11.4 c) 2.42 d) -0.91 e) 4.97

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LBS 271 Page 2 of 6 Final 2003 Problem 6 Two objects oscillate on springs in simple harmonic motion. Object 1 has mass M 1 , amplitude A 1 , and a spring with a spring constant k 1 . Object 2 has M 2 = 5·M 1 , A 2 = 2·A 1 , and k 2 = 1.5·k 1 . How do the total energies of these two systems compare? a) E 2 /E 1 = 1/6 b) E 2 /E 1 = 6 c) E 2 /E 1 = 5/6 d) E 2 /E 1 = 6/5 e) E 2 /E 1 = 30
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