An ambulance drove by Juku on the street. Juku noticed that when the ambulance passed him the tone of its siren fell below by a minor third. How fast did the ambulance drive? Near Juku the speed of sound in the air was vh=\SI343\meter\per\second. Assume that Juku’s distance from the linear trajectory of the ambulance is insignificantly small. The Doppler effect gives a relation between frequencies and velocities of motion.
fafv=vh+vavh+vv,
where fv is the observed frequency, fa the emitted frequency, vv the velocity of the receiver and va the velocity of the source.
Hint. Minor third is a musical interval that is a 3 semitone difference in a sound’s frequency. One octave means a 2 time difference in the sound’s frequency and is equal to 6 tones. Assume that the tones are divided in the octave so that if for three sound frequencies f1,f2,f3 applies f1f2=f2f3 and if between f1 and f2 there is one tone then between f2 and f3 there is also one tone.