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` .

Answer

A, B, C, D

Explanation

According to the question
`v=1500m/s`
`f=2000Hertz`
`v_s=10 m/s, v_0=15m/s`
So the apparent frequency heard by the submarine B
`=((1500+15)/(1500-10))xx(2000)`
`=2034Hz`
b. Apparent frequency received by submarine A
`=((1500+10)/(1500-15))xx(2034)`
`=2068 Hz`