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 train's speed is reduced to `17 m//s`, the frequency registered is `f_(2)`. If the speed of sound of `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

`n_(1)=n_(0)(340)/(340-34) =(10)/(9) n_(0)`
`n_(2)=n_(0)(340)/(340-17) =(20)/(19) n_(0)`
`(n_(1))/(n_(2)) =(10)/(9) xx(19)/(20) = (19)/(18)`.