su09EIIIS - Physics 53 Summer 2009 Exam III Solutions In...

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Physics 53 Summer 2009 1 Exam III Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols given, and standard constants such as g . If numbers are required, use g = 10 m/s 2 . Part A: Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. A hydraulic jack consists of a cylinder (1) with a small cross section area a , connected by a pipe to a cylinder (2) with larger cross section A . Each cylinder is fitted with a piston that can move vertically, and the system is filled with an incompressible fluid. A heavy load to be raised rests on the piston in 2; the total mass of the load and the piston is M . A force F 1 is exerted downward on the piston in 1, resulting in an upward force F 2 on the piston in 2 . Which of the following is NOT true? The pressure in both cylinders is the same. As the piston in 1 moves down distance d the piston in 2 moves up distance d ! ( a / A ) . To lift the piston in 2 and the load at constant speed, we must have F 1 = Mg ! ( A / a ) . [ F 1 = Mg ! ( a / A ) . The whole point of the device is that F 1 is less than Mg .] The work done by F 1 is equal to the work done by F 2 . 2. Waves 1 and 2 exist simultaneously in a medium, described by the functions y 1 ( x , t ) = 0.01cos(10 ! x " 100 ! t ) y 2 ( x , t ) = 0.01cos(9 ! x " 90 ! t ) Wave 1 travels faster than wave 2. [Same speed] Superposition of these waves produces a standing wave. The waves produce 5 beats/s. [Frequencies are 50 and 45 Hz] None of the above is true. 1 2
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Physics 53 Summer 2009 2 3. The frequencies of successive harmonics of an organ pipe are 250 and 350 Hz. The fundamental frequency for this pipe is 250 Hz. The fundamental frequency for this pipe is 50 Hz. The pipe is open at both ends. [Closed at one end] None of the above is true. 4. Two sounds produce loudness levels of 90 db and 60 db for a listener. The ratio of the intensities of these sounds is: 3/2.
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