The frequency of the whlstle of a train Is 512 Hz . Thetrain crosses a station at a speed of 72 km . h^(-1) Calculate the frequency of the sound heard by a Iistener, standing on the platform , before and after the train crosses the station. Neglect the effect of wind . Velocity of sound is 336 , m s^(-1) .

The frequency of the whlstle of a train Is 512 Hz . Thetrain crosses a

1.	The frequency of the whlstle of a train Is 512 Hz . Thetrain crosses a station at a speed of 72 km . h^(-1) Calculate the frequency of the sound heard by a Iistener, standing on the platform , before and after the train crosses the station. Neglect the effect of wind . Velocity of sound is 336 , m s^(-1) .
Answer» Solution :Velocity of the TRAIN ` = 72 km . `h^(-1)` ` = (72 xx1000)/(60xx60) m. s^(-1)` `= 20 m. s^(-1)` When the train approaches the station , the DISTANCE covered hy 512 sound waves = 336 - 20 = 316` m ` therefore ` Apparent wavelength , ` lambda . = (316)/(512) m ` ` therefore ` Apparent frequencydue to Doppler effect ` = (" velocity of sound (V))/(lambda .)` `(336)/((316)/(512)) = (336xx512)/(316) = 544.4 Hz ` ` Again , when the train recedes from the station , the distance covered y 512 sound waves= 366 + 20 = 356 m ` therefore ` Apparent wavelength , ` lambda . = (356)/(512) m` ` therefore ` Apparent freaquency= `(V) /(lambda .) = (336)/((356)/(512)) = (336xx 512)/(356) = 483.2 Hz .`