A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is `f_(1)`. If the speed of train is reduced to 17 m/s, the frequency registered is `f_(2)`. If speed fo sound is 340 m/s, then the ratio `f_(1)//f_(2)` is :

Options

A. `18//19`
B. `1//2`
C. 2
D. `19//18`

Answer

D

Explanation

Here, `v_(s_(1))=34 ms^(-1)` and `v=340 ms^(-1)`
`f_(1)=(vxxn)/(v-v_(s_(1)))=(340xxn)/(340-34)=340/306 n`
`f_(2)=(v xxn)/(v-v_(2))=(340xxn)/((340-17))=(340 n)/323`
`implies f_(1)/f_(2)=323/306=19/18`