CGPET 2015 Solved Paper

Generalised formula for apparent frequency is
fa=(

v±v0

v∓vs

)f0
According to the question source is stationary,
vs=0
fa=f′=(

v±v0

v

)f0
Observer is moving towards the source
⇒fa=f′(

v+v0

v

)f
where, v = speed of the wave
v0 = speed of the observer
f = original frequency of the source