A sounding body of negligible dimension emiting a frequency of 150 Hz is dropped from a height. During its fall under gravity it passes near a ballon moving up with a constant velocity of 2 m/s . One second after is started to fall , the difference in the frequency observed by the man in ballon just before and just after crossing the body will be (given that velocity of sound = 300 m/s , g = `10 m//s^(2)`)

Options

A. 12
B. 6
C. 8
D. 4

Answer

A

Explanation

`f=f_(0)((vpmv_(0))/(vpmv_(s)))`
When approaching `f_(a)=150[(300+2)/(300-10)]`
when receding `f_(r)=150[(300-2)/(300+10)]rArr f_(a)-f_(r)~=12` hence (A)