A train moves towards a stationary observer with speed `34 m//s`. The train sounds a whistle and its frequency registered by the obsrever is `f_(1)`. If the train's speed is reduced to `17 m//s`, the freuqncy 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

(d) `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)`