P18_056 - = f v + u D v + u S = f v + w v + w = 2000 Hz ....

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56. The Doppler shift formula, Eq. 18-47, is valid only when both u S and u D are measured with respect to a stationary medium (i.e., no wind). To modify this formula in the presence of a wind, we switch to a new reference frame in which there is no wind. (a) When the wind is blowing from the source to the observer with a speed w ,wehave u 0 S = u 0 D = w in the new reference frame that moves together with the wind. Since the observer is now approaching thesourcewh i
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Unformatted text preview: = f v + u D v + u S = f v + w v + w = 2000 Hz . In other words, there is no Doppler shift. (b) In this case, all we need to do is to reverse the signs in front of both u D and u S . The result is that there is still no Doppler shift: f = f v u D v u S = f v w v w = 2000 Hz . In general, there will always be no Doppler shift as long as there is no relative motion between the observer and the source, regardless of whether a wind is present or not....
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