An observer moves towards a stationary source of sound with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

Options

A. zero
B. `0.5%`
C. `5%`
D. `20%`

Answer

D

Explanation

Given `upsilon_(0)=(upsilon)/5rArr upsilon_(0)rArr upsilon_(0)d=320/5 =64 m//s`
When observer move towards the stationary source, then
`n'=((upsilon+upsilon_(0))/(upsilon))n`
`n'=((320+64)/320) n`
`n'=(384/320)n`
`(n')/n=384/320`
Hence, percentage increases,
`((n'-n)/n)=((384-320)/320xx100) %`
`=(64/320xx100)%`
`=20 %`