A fishing vessel uses a SONAR set to locate a school of fish.
(i) A short sound pulse sent from the surface returns after 0.28 s. If the speed of sound in sea water is 1500 m/s, determine the depth of the school of fish below the SONAR transducer.
(ii) The operator lowers the transducer to a depth of 4 m below the water surface and sends another pulse, which now returns in 0.272 s. Calculate the new depth of the school.
(iii) Explain briefly why lowering the transducer reduces the measured time even though the actual depth of the fish remains almost the same.