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Unformatted text preview: hernandez (ejh742) oldhomework 34 Turner (58120) 1 This printout should have 14 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Two similar tuning forks produce sound waves of the same 6 . 2 mPa amplitude. One tuning fork y 1 has a frequency 624 s 1 and the other y 2 has a frequency of 728 s 1 . These two tuning forks produce interference. + A + A AA T beat T wave y 1 y 2 y 1 + y 2 + A A 3 T beat 6 T beat What is the number of beats per second that is heard? Correct answer: 104 Hz. Explanation: Let : A = 6 . 2 mPa , f 1 = 624 s 1 , and f 2 = 728 s 1 . +12 12 A (mPa) t (milliseconds) 9 . 6 ms 19 . 2 ms y 1 y 2 y 1 + y 2 +12 12 A (mPa) t (milliseconds) 28 . 8 ms 57 . 6 ms Two harmonic waves are described by y 1 = A cos( k x 1 t ) and y 2 = A cos( k x 2 t ) . f 2 f 1 2 = 52 s 1 , f 1 + f 2 2 = 676 s 1 , T wave = 1 f 2 f 1 2 = 19 . 2 ms , 1 = 2 f 1 = 2 (624 s 1 ) = 3920 . 71 rad / s , 2 = 2 f 2 = 2 (728 s 1 ) = 4574 . 16 rad / s , 2 1 2 = 326 . 726 rad / s , 2 + 1 2 = 4247 . 43 rad / s , hernandez (ejh742) oldhomework 34 Turner (58120) 2 and y 1 + y 2 = 2 A cos bracketleftbiggparenleftbigg 1 2 2 parenrightbigg t bracketrightbigg cos bracketleftbiggparenleftbigg 1 + 2 2 parenrightbigg t bracketrightbigg A = 2 A cos bracketleftbiggparenleftbigg 1 2 2 parenrightbigg t bracketrightbiggvextendsingle vextendsingle vextendsingle vextendsingle max = 2 (6 . 2 mPa) cos bracketleftbigg ( 326 . 726 rad / s) t bracketrightbiggvextendsingle vextendsingle vextendsingle vextendsingle max = 12 . 4 mPa , where A is the amplitude of the sum of the two waves y 1 + y 2 , and A is the amplitude of either wave y 1 or y 2 . The wave produced by the interference of two waves of frequencies f 2 and f 1 , respec tively, has frequency f wave f 2 f 1 2 , where f 2 > f 1 = 728 s 1 624 s 1 2 = 52 s 1 , and the period T wave 1 f wave = 1 52 s 1 = 19 . 2 ms ....
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This note was uploaded on 06/14/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Physics, Work

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