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Homework Help: Special relativity of a light source moving downstream

  1. Nov 30, 2009 #1
    1. The problem statement, all variables and given/known data

    Let Cw be the speed of light through water at rest. Water is now flowing at speed v parallel to the x axis according to one observer, and there is also a light source moving with the water at speed v

    1) what is the speed at which the light source sends light signals in the downstream direction?
    2) what is the speed at which the light source sends light signals in the upstream direction
    3) What happens for the upstream light signal, if v<cw?

    a. the signal propagates in the positive x direction
    b.the signal propagates in the negative x direction
    c the signal propagates at zero speed

    2. Relevant equations

    3. The attempt at a solution

    i dont really know where to start. I was gonna use the equation

    but since we dont have the time
    im not really sure thanks in advance
  2. jcsd
  3. Dec 1, 2009 #2
  4. Dec 1, 2009 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: How do velocities add relativistically?
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