Physics 121 Dr. E. F. Redish Fall 2009 Sample Problems Final Exam 11. (20 pts) Two ladybugs are sitting on a rotating turntable and are going around without slipping. Both bugs have the same mass, but bug B is twice as far from the center as bug A. Use the coordinate system shown: the turntable is rotating about the z-axis and the x- and y-axes are in the plane of the disk. The axes cross at the zeroes of their variables. (The coordinate system does NOT rotate.) At time t = 0, both bugs lie on the x-axis. For the four physical variables below, identify which of the graphs in the figure below could represent that variable for both of the bugs if the scales on the axes were correct and put the number of the graph in the appropriate box on your answer sheet. The axes cross at the zeroes of their variables. (When only one line is shown, both bugs have identical graphs for that variable.) 1.1 The x-component of the friction force on the bugs; 1.2 The speed of the bugs; 1.3 The y-component of the velocity of the bugs; 1.4 The angular velocity of the bugs. 1. (30 points) An ideal gas is contained in an airtight box. Complete each of the following five statements below to show the quantitative change that will occur. For example, if you want to say that the volume, initially equal to V, quadruples, complete the statement with "4V". a. If the absolute temperature of the gas is halved, the average speed of a gas molecule, v0, becomes _____. b. If the average speed of a gas molecule doubles, the pressure, p, on a wall of the box becomes _____.Physics 121 Dr. E. F. Redish Fall 2009 Sample Problems Final Exam 2c. If the absolute temperature of the gas is halved, the pressure, p, on a wall of the box becomes _____. d. If the number of molecules in the box is doubled but the absolute temperature of the gas is kept the same, the average speed of a gas molecule, v0, becomes _____. e. If the number of gas molecules inside the box is doubled, but the temperature is kept the same, the pressure, p, on the wall of the box becomes _____. II. (25 points) Suppose we mix 40 g of water at 90 oC with 30 g of water at 10 oC. a. What will be the final temperature of the mixture? (10 pts) b. How much heat does each gram of hot water lose? How much does the temperature of each gram of hot water change? How much does the temperature of the entire sample of hot water change? (5 pts) c. How much heat does each gram of cold water gain? How much does the temperature of each gram of cold water change? How much does the temperature of the entire sample of cold water change? (5 pts) d. Are your results to the first part of b) and the first part of c) the same or different? Explain why. (5 pts) 2. (20 points) Three blocks are at rest in a tank of water in the positions shown. Each block has the same shape and size but they are made of different materials. Block A floats with part of its volume out of the water, block B can remain where it is shown, halfway down in the tank, and block C rests on the bottom. For each of the following four items, rank the quantity for the three blocks. For example, if the item were “volume”, since the volume of the blocks are the same, you would write “A=B=C.” If the item were “depth”, you would write “C > B > A”, since C has the largest depth, A the smallest, and B is in between. 2.1 Force pushing downward on the top of the blocks. 2.2 Force pushing upward on the bottom of the blocks. 2.3 Buoyant force the water exerts on the blocks. 2.4 Net force experienced by the blocks. 3. (20 pts) For each of the items below complete the sentence with quantitative words in the box on your answer sheet. Use words such as “not change”, “double”, “triple”, “halve”, etc. If you prefer, you may write, =, X2, X4, ÷2, ÷3, to mean equal, doubled, quadruples, halved, divided by three, etc. (Note that “increases” or “decreases” is NOT sufficient.) A B CPhysics 121 Dr. E. F. Redish Fall 2009 Sample Problems Final Exam 33.1 The interior of a water pipe bringing water into your hot water heater has narrowed as a result of the buildup of scale from the fact that your water is very hard (contains dissolved chemicals). The radius of the open area inside the pipe has decreased by a factor of two. If the pressure differential remains the same, the flow into the heater will _______. 3.2 You have a single window in the wall of your kitchen and you are contemplating putting a second identical window into that wall. In the winter, for a given inside-outside temperature difference, that change will ________ the flow of heat out of your house through the windows in that wall. 3.3 Blood is flowing through an artery that has a partial blockage in a part of the artery so that half its cross sectional area is blocked. In the part with the blockage, the velocity of the blood is ________ the velocity of the blood in the unblocked part of the artery. 3.4 I blow as hard as I can through a single straw. If instead, I blow as hard as I can through two straws (of the same length as the single straw) placed side by side, the rate of flow will ________. 5. (10 pts) For the partial statements below choose the letters of the phrases that complete the statements correctly. If more than one is correct, give them all. If none is correct, write N. 5.1 A news station shows a video of an astronaut in a space station. She is demonstrating a tool that she used to make a repair to the station during a spacewalk. When she releases the tool it floats in the air next to her. The reason it does this is: A. There is no gravity in the space station. B. The tool and the astronaut are both in free fall. C. The gravity of the astronaut cancels the gravity of the earth on the tool. D. The net force on the tool is zero. E. They are both moving at the same high velocity. 5.2 In Star Wars IV, Luke Skywalker is seen dropping an object on the planet Tatooine. If the video is analyzed to determine the acceleration of the falling object, one discovers that g = 9.80 m/s2, the same as one would find on earth. However, the radius of Tatooine is approximately twice that of the earth. A plausible justification that gTatooine gEarth is A. The value of g is a constant in all situations. B. Tatooine has 2 suns and 3 moons. C. The mass of Tatooine is four times that of earth and cancels the effect …
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