How to Calculate the Speed of an Approaching Vehicle Using Doppler Effect?

[BuBbLeS01]

Test tomorrow...please help!

Homework Statement

A student in a parked car honks the horn, which has a `proper' frequency of 310.00 Hz. An observer in an approaching vehicle measures the frequency of the sound to be 342 Hz. Calculate the speed of the approaching vehicle. Use 340 m/s as the speed of sound in air.

Homework Equations

The Attempt at a Solution

Fs = 310 Hz
Fo = 342 Hz
Vo = 0 m/s
V = 340 m/s
Vs = ?

I know
Vs = (Fs - Fo / Fs + Fo) * V
if the object is going away from the observer
but how I do calculate if the object is approaching the person?

 

[Doc Al]

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