Doppler effect

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mchristo@freemail.gr - 31 Mar 2008 15:52 GMT

hi, i want to ask what happens in the next case:

An airplane is moving with speed u1 smaller than the speed of sound
towards a still observer.When the plane is over the observer,it
accelerates and reaches a speed u2 larger than the speed of sound and
it goes away form the observer. I wanna ask when the plane changes its
speed,what does the observer hear?Apparently the Doppler effect can't
be used here.

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PD - 31 Mar 2008 18:54 GMT

On Mar 31, 9:52 am, mchri...@freemail.gr wrote:

> hi, i want to ask what happens in the next case:
>
[quoted text clipped - 4 lines]
> speed,what does the observer hear?Apparently the Doppler effect can't
> be used here.

Well, since the acceleration can't *all* happen directly overhead, I
suppose it depends a little on how far away from directly overhead the
acceleration starts, and how from away from directly overhead the
acceleration ends.

And sure the Doppler effect can be used here. Just not in the two-
equation form you get from a basic book treatment where the plane's
velocity doesn't change.

PD

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Natural Science Forum / Physics / General Physics / March 2008

Doppler effect