An indian submarine is moving in the Arabian sea with constant velocity. To detect enemy it sends out sonar waves which travel with velocity `1050(m)/(s)` in water. Initially the waves are getting reflected from a fixed island and the reflected waves are coming back to submarine. The frequency of reflected waves are detected by the submarine and found to be `10%` greater than the sent waves.
Now an enemy ship comes in front, due to which the frequency of reflected waves detected by submarine becomes `21%` greater than the sent waves.
Q. The velocity of enemy ship should be

Options

A. `50(m)/(s)` towards indian submarine
B. `50(m)/(s)` away from indian submarine
C. `100(m)/(2)` towards indian submarine
D. `100(m)/(s)` away from indian submarine

Answer

A

Explanation

`f'=f_0((v+v_2)/(v-50))`,`f''=f'((v+50)/(v-v_2))`
`f''=f_0(((v+v_2)(v+50))/((v-v_2)(v-50)))=1.21f_0`
[`21%` greater than sent waves]
we get `v_2=50(m)/(s)` towards indian submarine.