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. 20/19
B. 19/18
C. 21/20
D. 18/17

Answer

B

Explanation

`f=(V - V_(0))/(V - V_(s)) f_(0)`
`f_(1)=(340)/(340-34) f_(0)`, `f_(2) = (340)/(340-17)f_(0)1, f_(1)/(f_(2)) = (340-17)/(340-34) = (323)/(306) = (19)/(18)`