# Project #36404 - General Physics \$30 for 7 problems due tonight

3. (a) Calculate the wavelengths in air at 20 degrees Celsius for sounds

in the maximum range of human hearing. 20 Hz to

20,000 Hz.  (b) What is the wavelength of a 10-MHz ultra-sonic wave?

6. A person with his ear to the ground sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur?

[Speed of sound through Air is 343 m/s. Speed of sound through Concrete is 3,000 m/s]

13. (a) Estimate the power output of sound from a person speaking in normal conversation.  Assume the sound spreads roughly uniformly over a sphere centered on the mouth.  (b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint; Add intensities, not dB’s]

(Hint; A person speaking in normal conversation has a Sound Level of 65 dB and an Intensity of 3x10^-6  (W/m^2)

15. Expensive amplifier A is rated at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp. (b) Will the expensive amp sound twice as loud as the cheaper one?

40. What is the beat frequency if middle C (262 Hz) and C# (227 Hz) are played together? What if each is played two octaves lower (each frequency reduced by a factor of 4)?

53. A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25.0 m/s. Was is the received sound frequency?

58. A factory whistle emits sound of frequency 570 Hz. When the wind velocity is 12.0 m/s from the north, what frequency will observers hear who are located, at rest, (a) due north, (b) due south, (c) due east, and (d) due west, of the whistle? What frequency is heard by a cyclist heading (e) north or (f) west, toward the whistle at 15.0 m/s? Assume T=20 degrees C.

 Subject Mathematics Due By (Pacific Time) 07/25/2014 10:30 pm
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