Quiz1Problem1Solution

# Quiz1Problem1Solution - Physics-7A Lecture A Quiz 1 Problem...

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Physics-7A Lecture A Quiz 1 Problem 1 Solution Part (a) 30% This is a closed system, so we have: E A + E B = Q + W = 0 E A = 1750 J – 250 J = +1500J E B = -1500J Then the intermediate point for B is (1000 J, 100ºC). Either writing that, or pointing to the correct spot on the B graph was counted as a correct answer. Part (b) 30% No, A will not reach its boiling point. There are two ways to express the correct answer, both equally valid. Answer 1: At the intermediate point, T A = 70ºC, T B = 100ºC. Heat will continue to go from B to A, so T B goes down while T A goes up. Then the final temperature is somewhere between 70ºC and 100ºC. But the boiling point of A is 100ºC, and therefore the system must end up below the boiling point of A. So A remains a liquid. Answer 2: For A to get to its boiling point, it will have to gain 250 J. And the system is closed, so B looses 250 J. But then from the graph, T B = 50ºC. So B will end up at a lower temperature than A! This

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