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anandghegde

let the sound source fall through a distance h in time t. Let it emit a sound at this instant. Time taken by sound to travel back the distance h towards the man = h/320
but h = gt^2/2 = 5t^2
therefore
t + 5t^2 = 4
solving this quadratic in t we get t =3.77 s
Velocity of the source at this instant = gt = 37.7m/s
app frequency = 1000 (320)/{320+37.7}
= 894.6 Hz

So nearest ans is c

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