Frequency change:

$\overline{){{\mathbf{f}}}_{\mathbf{o}\mathbf{b}\mathbf{s}}{\mathbf{=}}{\mathbf{f}}{\mathbf{\left(}}\frac{{\mathbf{v}}_{\mathbf{w}}}{{\mathbf{v}}_{\mathbf{w}}\mathbf{\pm}{\mathbf{v}}_{\mathbf{s}}}{\mathbf{\right)}}}$

Where f_{obs} is the frequency perceived by the observer, f is the frequency of the source, v_{w} is the velocity of the wave, and v_{s} is the velocity of the source.

Suppose an oncoming ambulance moving at 115 km/h emits a steady 785-Hz sound from its siren

What frequency, in Hz, does she observe after the ambulance has passed? The speed of sound on this day is 345 m/s

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