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Help with moving emitter/receiver cutoff speed

  1. Oct 4, 2007 #1

    I'm working on a Mac application to visually illustrate the doppler effect and managed to confuse myself with the following problem. I'm sure it's an easy one but I've been looking at it too long and can't figure it out.

    Here's it is:

    Given two objects moving at the same speed along parallel paths on a plane, and a signal (say little marbles) being shot between them, where the time it takes for the signal to go from one object to the other is one second. If you accelerate the objects, at what speed, relative to the signal speed, would a signal from object "A" never arrive at object "B"?

    I tried drawing a circle from the center of object "A" through the center of object "B" and see from that, that if the objects are moving at the same speed as the signal, it would never arrive at "B" but the cutoff speed is some value less than one and I can't seem to figure it out.

    Can anyone help me untangle this?

    Thanks for any help
  2. jcsd
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