A SONAR system fixed in a submarine operates at a frequency 50 kHz. It is moving towards a rocky hill present inside water with a speed of 432 `km h^(-1)` . What is the apparent frequency of sound observed at the submarine after reflection by the rocky hill ?
(Take velocity of sound in water to be 1450 `m s^(-1)` )

Explanation

(i) Doppler effect ,
`n^(1) = ((v)/(v - v_(s))) , n^(11) = n^(1) ((v+v_(0))/(v))`
(ii) Consider the two cases .
In the first case , consider the submarine as the source and rocky hill the observer of sound .
Calculate the frequency as heard at the rocky hill using the experssion for apparent frequency (Doppler's effect) . The frequency of sound reflected by the rocky hill is the same as that incident on it . In the second case consider the rocky hill as the source and the submarine as the observer of sound .
Now find the apparent frequency of sound as heard at the submarine using the experssion for apparent frequency .
(iii) 59 Hz