In: Physics
2. A whale wants to detect a school of fish by sonar. The school is 20 m wide, and the speed of sound in seawater (density ρ = 1020 kg/m3 ) is 1500 m/s.
a) What is the minimum echolocation frequency that the whale should use to locate the fish?
b) Suppose that the fish are neutrally buoyant thanks to their swim bladders. What fraction of their body volume should be made of air? Assume that the density of the rest of the body (ignoring the swim bladder) is 1060 kg/m3 , and the density of air is 1.3 kg/m3 .
c) A clever fish might try to “acoustically camoflage” itself to sonar by matching its acoustic impedance to that of water. The speed of sound in the fish’s flesh is 1580 m/s. The speed of sound in the air of the swim bladder is 343 m/s. Discuss whether it might be possible to use the swim bladder to adjust the acoustic impedance of the fish to match that of the surrounding water. If this is possible, for what range of frequencies would this trick work?