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Homework Help: Doppler Effect of radar

  1. Mar 10, 2009 #1
    1. The problem statement, all variables and given/known data
    A radar beam has a wavelength of .02 m. The frequency is 17500 Hz. What would be its echo frequency if a rocket 60km away is moving at 500m/s and the radar is coming from a jet moving at 310m/s towards the rocket which is aimed at it? (b) Would the rocket appear red shifted or blue shifted? (c) Which would be shifted more, a sound wave or a light wave?

    2. Relevant equations
    [fo/vw + vo] = [fs/vw + vs]

    3. The attempt at a solution

    [fo/vw + vo] = [fs/vw + vs]
    = [fo/ (350 + 310 + 500)] = [17500/ (350 + 310 - 500)]
    fo = 126875Hz

    (b) Blue shifted

    (c)Sound wave
    Is this correct?
    Last edited: Mar 10, 2009
  2. jcsd
  3. Mar 10, 2009 #2


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    Homework Helper

    No. The answer must be larger than 17 500 Hz.
    Why do you have three velocities on each side when the formula only asks for two?
    Both the 310 and the 500 must act to make the return frequency larger; make sure they have the correct signs to accomplish that.
    It looks like you are using 350 m/s for the speed of radio waves - not correct!
  4. Mar 10, 2009 #3
    What do you think would happen if a wave of a certain wavelength tries to fit in to a smaller gap than the original separation of the moving objects??
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