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Homework Help: Doppler shift of an approaching source with interference problem

  1. Dec 8, 2011 #1
    1. The problem statement, all variables and given/known data

    P15. The police car with its 300 Hz siren is moving toward a warehouse at 30 m/s, intending to crash through the door. What frequency does the driver of the police car hear reflected from the warehouse? (5 marks)

    2. Relevant equations
    doppler shift for an approaching source. (f+) = fo / [1-vs/v]

    3. The attempt at a solution

    the doppler shift of the siren at the door is (300Hz)/ (1- [(30m/s)/(343m/s)]) =328.75Hz

    now assume that the warehouse/ warehouse door reflects 100% of the incident waves.

    I really have no idea where to go from here.
  2. jcsd
  3. Dec 8, 2011 #2


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    For reflected waves, treat source at rest and the observer is moving towards the source with the velocity equal to the velocity of the police car.
  4. Dec 8, 2011 #3

    Simon Bridge

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    The warehouse reflects each wave that hits it, and becomes a source.
    The car is driving through the reflected waves.
  5. Dec 10, 2011 #4
    hey guys thanks for the reply I tried it and it worked.
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