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And one last easy example to finish it off
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so once again, we are looking for v_source
this time though not only is the police car
who is the source of the sound moving towards you
your car is also moving
and you are the observer, so we have both v_s and v_obs, so this is where we
use that combined form
let's reason it out whether it is suppose to be + or -
considering the source is moving towards us, the frequency is going to go up, so to get that we need the denominator to be smaller
so v_s we have a - underneathe
and then on top, we have
we are moving towards the source, the frequency should be higher, so therefore the numerator should be positive
knowing everything else, I would just sub it right in ...
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the rest is just math
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which happens to be
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and that's it, as long as you know
which one is the source, which one is the observer, what's doing the moving, these are fairly straight forward