Two submarines are underwater and approaching each other head-on. Sub A has a speed of 12 m/s and sub B has a speed of 17 m/s. Sub A sends out a 1520 Hz sonar wave that travels at a speed of 1522 m/s. ... I already solved for this question ... ... What is the frequency of the sound detected by sub B (to the nearest Hz)? ... ... I used the Doppler equation and I got 1549 Hz as an answer, which is correct. ... My next question is ... ... Part of the sonar wave is reflected from B and returns to A. What frequency does A detect for this reflected wave (to the nearest Hz)? ... do I use the Doppler equation again ... or is there a reflection equation or concept that I missed out on?