The Pitch of the whistle of an engine appears to drop to `5/6` th of original value when it passes a stationary observer if the speed of sound in air is 350 m/s then the speed of engine is

Options

A. 35 m/s
B. 70 m/s
C. 105 m/s
D. 140 m/s

Answer

B

Explanation

`n' = (5)/(6) n`
`n' = n [(V)/(V = V_(s))]`
`(5)/(6) n = n [(V)/(V + V_(s))]`
`:. V + V_(s) = (V)/(5//6) = (6V)/(5)`
`V_(s) = (6)/(5) V - V = (1)/(5)V`
`:. V_(s) = (V)/(5) = (350)/(5) = 70 m//s`