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Calculating doppler shift

  1. Aug 12, 2012 #1
    A police car is traveling at a constant speed of 100. km/h with a radar gun which generates and detects radiowaves. The police car and the ambulance drive directly towards each other. The radar gun produces radiowaves with a wavelength of 0.0650 m.

    What doppler shift (Δf = f′–f) is detected by the radar gun after the radiowave has been reflected by the ambulance?

    I don't really know what to do. Do I use the relative speed between the police car and ambulance which is 180kmph? The right answer is 1540 Hz.
     
  2. jcsd
  3. Aug 12, 2012 #2

    Simon Bridge

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    You have to walk yourself through the steps - the police car is acting as a transmitter of the original wave, and a receiver of the reflected wave, and it's moving.

    Personally, since radio waves are light, I'd use the relative speed and the relativistic Doppler shift. F it were sound you may have to account for the medium.
     
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