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Unformatted text preview: khounvivongsy (sk27799) Extra Credit Weathers (17104) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Given: specific heat of water c w = 4180 J / kg C A 283 kg cast-iron car engine contains wa- ter as a coolant. Suppose the engines tem- perature is 33 C when it is shut off and the air temperature is 13 C. The heat given off by the engine and water in it as they cool to air temperature is 4 . 5 10 6 J. (Assume the specific heat of iron is 450 J / kg C.) What mass of water is used to cool the engine? Correct answer: 23 . 3612 kg. Explanation: Given : Q lost = 4 . 5 10 6 J , T h = 33 C , T l = 13 C , c e = 450 J / kg C , c w = 4180 J / kg C , and m e = 283 kg . Q lost = m w c w T w + m e c e T e , where T = T w = T e = T h- T l . Thus m w c w T = Q lost- m e c e T m w = Q lost- m e c e T c w T = Q lost c w T- m e c e c w = 4 . 5 10 6 J (4180 J / kg C)(20 C)- (283 kg) (450 J / kg C) 4180 J / kg C = 23 . 3612 kg . 002 10.0 points A 214 kg student eats a 200 Calorie doughnut. To burn it off, he decides to climb the steps of a tall building. (1 food Calorie = 10 3 Calories.) The acceleration of gravity is 9 . 8 m / s 2 . How high would he have to climb to expend an equivalent amount of work? Correct answer: 399 . 199 m. Explanation: Given : m = 214 kg , and E = 200 Calorie . At the height of h , he has gained a potential energy of E p = mg h, To burn it off, he needs to do that amount of work; i.e. , E p = E = mg h, h = E mg = (200 Calorie)(1000 cal /...
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- Fall '09