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?

Explanation

Here, the observer `//` listener moves towards a stationary source `: v_(L)=-v//5, v_(s)=0`.
`v^(')=((upsilon-upsilon_(L))//v)/(upsilon-upsilon_(s))=((upsilon+upsilon//5)v)/(upsilon)=(6)/(5)v=1.2v.`
`%` age increase in frequency
`=((v^(')-v)100)/(v)=((1.2v-v)100)/(v)=20%`