The apparent frequency of the whistle of an engine changes in the ratio `9 : 5` as the engine passes the stationary observer. If the velocity of sound is `350 ms^(-1)`, then the speed of the engine is

Options

A. `9 0 ms^(-1)`
B. `50 ms^(-1)`
C. `100 ms^(-1)`
D. `70 ms^(-1)`

Answer

C

Explanation

`(n'_(1))/(n'_(2)) = (v + v_(s))/(v - v_(s))`
`(9)/(5) = (v + v_(s))/(v - v_(s))`
`9v - 9v_(s) = 5v + 5v_(s)`
`4v = 14 v_(s)`
`v_(s) = (4 xx 350)/(14) = 100`