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Doppler Effect of a blown whistle

  1. Apr 27, 2009 #1
    1. The problem statement, all variables and given/known data
    A whistle of frequency 500 Hz tied to the end of a string of length 1.2 m revolves at 400 rev/min. A listener standing some distance away in the plane of rotation hears frequencies in the range ____?
    (speed of sound=340 m/s)
    a) 436 to 586
    b) 426 to 574
    c) 426 to 584
    d) 436 to 674


    2. Relevant equations



    3. The attempt at a solution
    I'm not really sure how to approach this particular problem...i'm lost especially for the units and what to do with the string...thanks
     
  2. jcsd
  3. Apr 27, 2009 #2

    rl.bhat

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    when the whistle is moving in a horizontal circle, at two points on the circle the whistle is moving either towards the observer or away from him. Apply Doppler effect to find the frequencies.
     
  4. Apr 28, 2009 #3
    okay i understand that part, but how do i convert 400 rev/min and for the length of the string do i use C=2(pi)radius and solve for r?
     
    Last edited: Apr 28, 2009
  5. Apr 28, 2009 #4

    rl.bhat

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    Velocity v = 2*pi*n*r where n is the number revolution per second.
     
  6. Apr 28, 2009 #5
    but how do i solve for the radius using the length of the string?
     
  7. Apr 28, 2009 #6

    rl.bhat

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    Length of the string itself is the radius.
     
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