COMEDK Exam 2017 Solved Paper

Let fs be the frequency of source.
The apparent frequency heard when listener moves towards source is
f′=fs(‌

vs+vo

vs

)
⇒‌‌200=fs(‌

vs+40

vs

) . . . (i)
The apparent frequency heard, when listener moves away from source is
f′′‌=fs(‌

vs−vo

vs

)
⇒‌‌160‌=fs(‌

vs−40

vs

) . . . (ii)
Dividing Eq. (i) by Eq. (ii), we get
‌‌

200

160

=‌

vs+40

vs−40

‌⇒‌‌‌

5

4

=‌

vs+40

vs−40

‌⇒‌‌5vs−200=4vs+160
‌⇒‌‌vs=360m∕ s
‌