# ps13c35 - Ph 111.01 December 5 2008 PS 13c(35 Problem 1 =...

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Ph 111.01 December 5, 2008 PS 13c (35) Problem 1 = Walker P. 16-22. When people sleep, their metabolic rate is about 2.6 10 -4 C/(s · kg). How many Calories does a 63 kg person metabolize while sleeping 7.0 hours? Cal Q=RMt Solution. The rate constant given implies the equation below. () ( ) 4 0 Cal/(s-kg) 63 kg 7 3600 s 413 Cal x x = 2.6 1 QR M t == Problem 2 = Walker P. 16-36. A blacksmith drops a 0.45 kg iron horseshoe into a bucket containing 25 kg of water. m h m w T w T h (a) If the initial temperature of the horseshoe is 475 °C, and the initial temperature of the water is 45 °C, what is the equilibrium temperature of the system? Assume no heat is exchanged with the surroundings. °C (b) Suppose the 0.45 kg iron horseshoe had been a 2.0 kg lead horseshoe instead. Would the equilibrium temperature in this case be greater than, less than, or the same as in part (a)? ---Select--- Solution. (a) We use the “conservation of heat” equation, ( ) h h www h ww hh mcT mcT mc mc T += + giving for the final temperature T ( ) ( ) ( ) ( ) ( ( ) ( ) ( ) ) w w w hw w 0.45 kg 448 J/(kg-C 475 C 25 kg 4168 J/(kg-C 45 C 0.45 kg 448 J/(kg-C 25 kg

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ps13c35 - Ph 111.01 December 5 2008 PS 13c(35 Problem 1 =...

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