Solution

A train is approaching a station at $90\,\mathrm{km\,h^{-1}}$, sounding a whistle of frequency $1000\,\mathrm{Hz}$. What will be the apparent frequency of the whistle as heard by a listener sitting on the platform? What will be the apparent frequency heard by the same listener if the train moves away from the station with the same speed? (Speed of sound is $340\,\mathrm{m\,s^{-1}}$)