An underwater acoustic research sonar transducer acts as a point source, emitting pressure waves uniformly in all directions through the ocean. At a distance of 12.0 m from the transducer, the displacement amplitude of the water molecules is detected to be 60 μm60\,\mu\text{m}60μm.
What is the displacement amplitude of the water molecules at a distance of 40.0 m from the transducer?
5.4 μm5.4\,\mu\text{m}5.4μm
18 μm18\,\mu\text{m}18μm
33 μm33\,\mu\text{m}33μm
200 μm200\,\mu\text{m}200μm
