Two submarines are underwater and approaching each other head-on. Sub A has a speed of 16 m/s and sub B has a speed of 5 m/s. ?

Question

Sub A sends out a 1440 Hz sonar wave that travels at a speed of 1522 m/s.

(a) What is the frequency of the sound detected by sub B?

 Hz

(b) Part of the sonar wave is reflected from B and returns to A. What frequency does A detect for this reflected wave?

 Hz

Answer 1

f = F₀*(V + Vr)/(V + Vs) ← Doppler

Vr +ve if rcvr moving toward src, Vs -ve if src moving toward rcvr

(a) f = 1440Hz * (1522+5) / (1522-16) = 1460 Hz

(b) f ' = 1460Hz * (1522+16) / (1522-5) = 1480 Hz

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