A siren emitting a note of frequency n is fitted on a police van, travelling towards a stationary listener. What is the velocity of the van, if the frequency of the note heard by the listener is double the original frequency?

Options

A. `V_(S) = V`
B. `V_(S) = (V)/(2)`
C. `V_(S) = 2V`
D. `V_(S) = (V)/(3)`

Answer

B

Explanation

`n' = ((V)/(V - V_(S))) n :. 2n = ((V)/(V - V_(S)))n`
`:. 2V - 2V_(S) = V :. V = 2V_(S) or V_(S) = (V)/(2)`