The apparent frequency of the whistle of an engine changes in the ratio `13 : 12` as the engine passes a stationary observer. If the velocity of sound is 350 m/s. The velocity of engine is

Options

A. 14 m/s
B. 16 m/s
C. 18 m/s
D. 20 m/s

Answer

A

Explanation

`(n'_(1))/(n'_(2)) = (v + v_(s))/(v - v_(s))`
`(13)/(12) = (v + v_(s))/(v - v_(s))`
`13v- 13v_(s) = 12 + 12 v_(s)`
`25v_(s) = v`
`v_(s) = (v)/(25) = (350)/(25) = 14 m//s`