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Unformatted text preview: Niu (qn269) HW12 Tsoi (58020) 1 This printout should have 19 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points At 15 C, an aluminum ring has an inner di ameter of 7 cm and a brass rod has a diameter of 7 . 06 cm. If the temperature coefficient of expansion for brass is b = 1 . 9 10 5 ( C) 1 and the temperature coefficient of expansion for alu minum is a = 2 . 4 10 5 ( C) 1 , to what temperature must the ring be heated so that it will just slip over the rod? Correct answer: 372 . 143 C. Explanation: Given : T = 15 C , d a = 7 cm , d b = 7 . 06 cm , b = 1 . 9 10 5 ( C) 1 , and a = 2 . 4 10 5 ( C) 1 . The new length will be d b = d a (1 + T ) d b = d a + d a T T 1 = T + T = T + d b d a d a a = 15 C + 7 . 06 cm 7 cm (7 cm)(2 . 4 10 5 ( C) 1 ) = 372 . 143 C . 002 (part 2 of 2) 10.0 points To what temperature must both be heated so that the ring just slips over the rod? Correct answer: 1787 C. Explanation: We need L Al = L brass for some T . Using the same law, L Al (1 + a T ) = L brass (1 + b T ) d a + d a a T = d b + d b b T T = T + d b d a a d a b d b a d a b d b = bracketleftbig 2 . 4 10 5 ( C) 1 bracketrightbig (7 cm) bracketleftbig 1 . 9 10 5 ( C) 1 bracketrightbig (7 . 06 cm) = 3 . 386 10 5 m / C so T = T 2 T T 2 = T + T = T + d b d a a d a b d b = 15 C + 7 . 06 cm 7 cm 3 . 386 10 5 m / C = 1787 C . 003 (part 1 of 2) 10.0 points An ideal gas occupies a volume of 366 cm 3 at 98 C and a pressure of 594 Pa. Determine the number of moles of gas in the container. Correct answer: 7 . 04785 10 5 mol. Explanation: Given : V = 366 cm 3 = 0 . 000366 m 3 , T = 98 C = 371 K , P = 594 Pa , R = 8 . 31451 J / Kmol , and N A = 6 . 02 10 23 mol 1 . Using the equation P V = nRT , the number of moles of gas in the container is n = P V RT = (594 Pa) ( . 000366 m 3 ) (8 . 31451 J / Kmol) (371 K) = 7 . 04785 10 5 mol . Niu (qn269) HW12 Tsoi (58020) 2 004 (part 2 of 2) 10.0 points Calculate the number of molecules in the con tainer....
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 Spring '09
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 Physics

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