A train approaching a platform at a speed of `54 km h^-1` sounds a whistle. An observer on the platform finds its frequency to be 1620 Hz. The train passes the platform keeping the whistle on and without slowing down. What frequency will the observer hear after the train has crossed the platfrom ? The speed of sound in air `= 332 ms^-1`

Answer

A, D

Explanation

Here given Apparent frequency
=1620Hz
so origiN/Al frequency of the train is given by
`120=((332+0+0()/(332-16))f`
`rarr =((1620xx317)/332))Hz`
`(where p=origiN/Al frequency)
So, apparent frequency of the tran observed by the observer in f
`=((332+0+0)/332+15)xx(1620x317)/332)`
`=317/347xx1620=1480Hz.