A passenger is standing on a platform. A train is arriving with speed =100m/s. It whistles at point B while the passenger is at point A. What is the frequency heard by the passenger if the whistle frequency is 100Hz? Speed of sound = 330m/s.

The Doppler effect or Doppler shift is the apparent change in frequency of a wave in relation to an observer moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842