A SONAR system fixed in a submarine operates at a frequency 40.0 kHz. An enemy submarine moves towards the SONAR with a speed of 360 km/h. What is the frequency of sound reflected by the submarine? Take the speed of sound in water to be 1450 m/sec.

Given:
OperatingfrequencyoftheSONARsystem,ν=40kHz
Speedoftheenemysubmarine,ve=360km/h=100m/s
Speedofsoundinwater,v=1450m/s
Thesourceisatrestandtheobserverenemysubmarineismoving
towardsit.Hence,theapparentfrequencyν'receivedandreflected
bythesubmarineisgivenby:
ν=v+vevν=1450+1001450×40=42.76kHz
Thefrequencyν''receivedbytheSONARis:
ν''=vv+vsν'
where,νs=100m/s
ν''=14501450100×42.76=45.93kHz