A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. Velocity of sound is 330 m/s. The number of beats heard by an observer standing behind the source is nearly

The observer hears a direct sound. In this case, the source is moving away from the observer' The apparent frequency Y n' is given by n′=nvv+vs=256330330+5=256330335 The observer also hears the reflected sound' In this case, the echo source is moving to wards the stationary observer. The apparent hequency n' is given by n′′=nVV−Vs=256330330−5=256330325 ∴  Beat frequency =n′′−n ′=256330325−330335