Question

A car moves at 20 m/s north. An ambulance passes it going 25 m/s north, with its siren on, f = 500 Hz. Find the frequency heard in the car when the ambulance is moving away. (The speed of sound in air is 343 m/s)

Answer 1

When source is is moving away from observer and observer approaching source

f" = (V+Vo)/(V+Vs) *f

Where, vs = Velocity of the Source,
           vo = Velocity of the Observer,
           v = Velocity of sound or light in medium,
           f = Real frequency,
           f' = Apparent frequency.

=>f" =(343+20)/(343+25)*500 = 493.20Hz