Two sirens situated one kilometer apart are producing sound of frequency 330 Hz. An observer starts moving from one siren to the other with a speed of 2 m/s. If the speed of sound be 330 m/s, what will be the beat frequency heard by the observer

Observer is moving away from siren 1 and towards the siren 2.Hearing frequency of sound emitted by siren 1n1=nv−v0v=330 330−2330=328HzHearing frequency of sound emitted by siren 2n2=n v+v0v=330 330+2330=332HzHence, beat frequency =n2−n1=332−328=4.