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

By using `n' =n((v)/(v-v_S))`
`impliesf_1=n((v)/(v-V_S))=n((340)/(340-34))=(340)/(306)n`
and `f_2=n((340)/(340-17))=n((340)/(323))implies(f_1)/(f_2)=(323)/(306)=(19)/(18)`.