Given:
f = 40 kHz v = 1450ms-1
Speed of enemy submarine = v0 = 360 km/ hr
=360 ×5/16 =100 m/s
Apparent frequency of sound waves:
(source at rest and observer moving towards the source)
Now this frequency is reflected by the enemy submarine and is observed by the SONAR
Note: Here the observer (SONAR) is at rest and the source is moving towards the observer at a speed of 360 km h-1 = 100 ms-1(vs)