SomeFinalExamPracticeQuestions

# SomeFinalExamPracticeQuestions - Questions for 7A practice...

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A B C Questions for 7A practice: 1. It is hot today and you stayed up all last night studying so you really need a cup of iced coffee. First, you make m coffee = 250g of hot coffee (the coffee starts out at T hot coffee = 90 ° C). You pour this hot coffee into an insulated container that already has ice in it. You like your coffee very cold so your problem is to decide how much ice you needed to put into the insulated container so that your coffee cools to exactly 0 ° C. You know that the ice has a temperature of T cold ice = -28 ° C when it is first taken out of your freezer and put into the container. The problem here is to determine the minimum amount of ice, m ice , that you need to put into the container so that your coffee gets to 0 ° C just as the last of the ice melts away. Assume that the insulated container itself has a very small heat capacity so that any energy transferred from it or to it is negligible and can be ignored. a) As appropriate, choose one or more physical systems and draw a complete energy-interaction diagram for each physical system that you chose. b) Write an algebraic equation (no numbers, only use symbols) expressing conservation of energy for each physical system that you chose. c) Plug the appropriate numbers into your equation(s) from part c) and find the minimum amount of ice, m ice , so that the hot coffee barely gets down to 0 ° C. 2. The picture to the right shows a box, which is released from rest and slides down the frictionless surface shown. There are three possible paths shown. If there is no air resistance, which path is most reasonable? a) A b) B c) C d) B or C are both reasonable e) not enough information. 3. The picture to the right shows a loop-the-loop track. A ball released from rest at the top of the track rolls down the track, up around the loop, and flies off the track to the right at the bottom. a) Neglecting air resistance, discuss the energy changes between point A and point B. That is, make a complete energy-interaction diagram taking the initial time to be when the ball is at point A and the final time when the ball is at point B. Draw graph of potential energy vs height. Then draw a graph of kinetic energy vs height. b) Neglecting air resistance, discuss the energy changes between point B and point C. That is, make a complete energy-interaction diagram taking the initial time to be when the ball is at point B and the final time when the ball is at point C. c) Answer part a) again but now include the effects that air resistance would have. d) Draw graph of potential energy vs height e) Then draw a graph of kinetic energy vs height A C B

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4. The picture to the right shows two wooden blocks (sitting on a wooden tabletop) connected to each other by a spring. The potential energy of the spring is shown (in the graph below the picture) as a function of the total length, L, of the spring. The blocks are released from rest with a separation L = 15 cm. a.
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## This note was uploaded on 01/05/2011 for the course PHY 7A taught by Professor Pardini during the Winter '08 term at UC Davis.

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SomeFinalExamPracticeQuestions - Questions for 7A practice...

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