12_InstSolManual_PDF_Part13

12_InstSolManual_PDF_Part13 - Mechanical Waves and Sound...

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(b) so This is about 31,000 times faster than the speed in Problem 12.46b. Reflect: Even though the sound wave intensity level is very high, the rate at which energy is delivered to the eardrum is very small, because the area of the eardrum is very small. 12.48. Set Up: with Solve: (a) gives and (b) (c) gives and (d) Intensity obeys the inverse square law but noise level does not. 12.49. Set Up: Example 12.9 shows that Solve: (a) gives and (b) gives (c) gives Reflect: Every doubling of the intensity increases the decibel level by 3.0 dB. 12.50. Set Up: The other player’s note can be either larger or smaller than 440 Hz. Solve: so the other player’s note could have frequency or 12.51. Set Up: Solve: 12.52. Set Up: and Solve: so 14 beats each second. 12.53. Set Up: Solve: (a) The frequency of the other propeller differs by 2.0 Hz, so the frequency of the other propeller is either 11.6 Hz or 7.6 Hz. These frequencies correspond to 696 rpm or 456 rpm. (b) When the speed and rpm of the second propeller is increased the beat frequency increases, so the frequency of the second propeller moves farther from the frequency of the first and the second propeller is turning at 696 rpm.
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