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ch 7 hw 3

# ch 7 hw 3 - Ch7 HW3 f10 Page 1 of 3 WebAssign Ch7 HW3...

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Web Assign Ch7 HW3 f10 (Homework) Ashlyn Baum Physics 303K, section B, Fall 2010 Instructor: Jim Chelikowsky Current Score : 18 / 18 Due : Wednesday, October 27, 2010 11:30 PM CDT 1. 6/6 points Question: MI3 7.5.P.046 170 grams of boiling water (temperature 100 ° C, heat capacity 4.2 J/gram/K) are poured into an aluminum pan whose mass is 850 grams and initial temperature 26 ° C (the heat capacity of aluminum is 0.9 J/gram/K). (a) After a short time, what is the temperature of the water? T final = 61.72 61.7 ° C (b) What simplifying assumptions did you have to make? (c) Next you place the pan on a hot electric stove. While the stove is heating the pan, you use a beater to stir the water, doing 26647 J of work, and the temperature of the water and pan increases to 87.1 ° C. How much energy transfer due to a temperature difference was there from the stove into the system consisting of the water plus the pan? Q = 10890.02 10900 J Solution or Explanation (a) Change of thermal energy = W + Q . The change of thermal energy of the water and pan is m water C water ( T 2 -100) + m Al C Al ( T 2 - T 1 ) = W + Q , and W = 0 and Q = 0, assuming that the water and pan reach thermal equilibrium quickly enough that there is little energy transfer due to a temperature difference to or from the surroundings. Solve for the unknown final temperature.

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