Two submarines are approaching each other in a calm sea. The first submarine travels at a speed of 36 km h^-1 and the other at 54 km h^-1 relative to the water. The first submarine sends a sound signal (sound waves in water are also called sonar) at a frequency of 2000 Hz. (a) At what frequency is this signal received by the second submarine ? (b) The signal is reflected from the second submarine. At what frequency is this signal received by the first submarine. Take the speed of the sound wave in water to be 1500 m s^-1 .
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According to the question <br> `v=1500m/s` <br> `f=2000Hertz` <br> `v_s=10 m/s, v_0=15m/s` <br> So the apparent frequency heard by the submarine B <br> `=((1500+15)/(1500-10))xx(2000)` <br> `=2034Hz` <br> b. Apparent frequency received by submarine A <br> `=((1500+10)/(1500-15))xx(2034)` <br> `=2068 Hz`