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Unformatted text preview: homework 13 KIM, JI Due: Nov 28 2007, 4:00 am 1 Question 1, chap 20, sect 2. part 1 of 1 10 points The concrete sections of a certain super highway are designed to have a length of 28 m. The sections are poured and cured at 12 C. What minimum spacing should the engi neer leave between the sections to eliminate buckling if the concrete is to reach a temper ature of 28 C? Correct answer: 0 . 005376 m (tolerance 1 %). Explanation: Let : L = 28 m , T 1 = 12 C , T 2 = 28 C , and = 1 . 2 10 5 ( C) 1 . The extension for this temperature interval will be L = L T = (28 m) bracketleftbig 1 . 2 10 5 ( C) 1 bracketrightbig (16 C) = . 005376 m . Question 2, chap 20, sect 2. part 1 of 2 10 points A copper rod and a steel rod are heated. At 0 C the copper rod has a length of L C , the steel one has a length of L S . When the rods are being heated or cooled, a difference of 4 . 6 cm is maintained between their lengths. Find the value of L C . Correct answer: 8 . 43333 cm (tolerance 1 %). Explanation: Let : d = 4 . 6 cm , C = 1 . 7 10 5 ( C) 1 , and S = 1 . 1 10 5 ( C) 1 . For d = L S L C = 4 . 6 cm to be constant, the rods must expand by equal amounts: C L C T = S L S T L S = C L C S d = C L C S L C S d = C L C S L C , so L C = S d C S = bracketleftbig 1 . 1 10 5 ( C) 1 bracketrightbig (4 . 6 cm) 1 . 7 10 5 ( C) 1 1 . 1 10 5 ( C) 1 = 8 . 43333 cm . Question 3, chap 20, sect 2. part 2 of 2 10 points Find the value of L S . Correct answer: 13 . 0333 cm (tolerance 1 %). Explanation: L s = L c + d = 8 . 43333 cm + 4 . 6 cm = 13 . 0333 cm ....
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 Fall '08
 Turner
 Physics, Work

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