Here, frequency of SONAR (Source) = 40 kHz = 40 x 103 Hz
Speed of sound waves (v) = 1450 ms-1
Speed of the observer, (v0) = 360 km h-1
= 360 x 5/18 ms-1 = 1000 ms-1
Since the source is at rest and the observer moves towards the source (SONAR)
We have,
This frequency (v') is reflected by the enemy ship and is observed by the SONAR (which now acts as observer). Therefore, in the case, vs = 360 km h-1 = 100 ms-1
Apparent frequency,