A train sounding a whistle of frequency 510 Hz approaches a station at 72 ~km / hr . The frequency of the note heard by an observer on the platform as the train (1) approaches the station and then (2) recedes the station are respectively (in hertz) (velocity of sound in air =320 ~m / s )

Step-by-step solution

Given, Frequency of source (n₀ )=510 ~Hz Velocity of source =72 ~km / hr =72 5 18 =20 ~m / s Velocity of sound in air =320 ~m / s Doppler formula for apparent frequency, when source is approaching a stationary listener, n₁=n₀ ( v v-v_s ) n ₁=510 ( 320 320-20 )=544 ~Hz Doppler formula for apparent frequency, when source is moving away from a stationary listener, aligned & n ₂= n ₀ ( v v + v _ s ) & n ₂=510 ( 320 320+20 )=480 ~Hz aligned