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Sound problem, clarify please

  1. Jun 9, 2012 #1
    Polly the parrot wants to escape from her enclosure at the zoo. The enclosure has a glass door and by tapping on the door with her beak Polly has been able to determine that the natural resonant frequency of the door is 900 Hz. The highest frequency squawk Polly can muster is 850 Hz but at one time she belonged to a Physics professor (Don’t ask how she ended up in the zoo!) so Polly knows about the Doppler effect.

    a. Find a value for how fast Polly will have to fly toward the glass so that her Doppler- shifted squawk matches the resonant frequency of the door. Assume that the speed of sound is 343 m/s.

    b. If the sound intensity level needed to break the glass is 110 dB and Polly wants to be able to break the glass from a distance of 1.0 m, find a value for the power in Watt of her squawk that will be required to achieve this. You may assume that Polly is a point source of sound.

    so i've got A which is 21.05ms^-1 (not sure if it's right), by using the formula Fd=((V/(V-Vs))*Fs.
    And for section B what i've tried is using the equation beta = (10log(I/Io), i know the area, and the decibel, but how am i suppose to get power in watts?

    thanks for the help
     
  2. jcsd
  3. Jun 9, 2012 #2

    ehild

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    You need to know the power belonging to Io.

    ehild
     
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