Waterfall acoustics. The turbulent impact of the water in a waterfall causes the surrounding ground to oscillate in a wide range of low frequencies. If the water falls freely (instead of hitting rock on the way down), the oscillations are greatest in amplitude at a particular frequency fm. This fact suggests that acoustic resonance is involved and fm is the fundamental frequency. The following table gives, for nine U.S. and Canadian waterfalls, measured values for fm and for the length of the water's free fall. Using waterfall 7, find the speed of sound if waterfall resonance is effectively like that in a tube with (a) two open ends and (b) only one open end. The speed of sound in turbulent water filled with air bubbles can be about 25% less than the speed of 1400 m/s in still water. (c) From the answers to (a) and (b), determine how many open ends are effectively involved in waterfall resonance. WATERFALL m (Hz) L (m) 1 23 4 5.6 3.8 80 6.1 97 71 53 49 5 6 7 8 9 8.8 6.0 19 21 40 35 24 13 11 8 (a) Number Units (b) Number Units Units (c) Number A certain loudspeaker system emits sound isotropically with a frequency of 1610 Hz and an intensity of 0.885 mW/m at a distance of 6.19 m. Assume that there are no reflections. (a) What is the intensity at 32.8 m2 At 6.19 m, what are (b) the displacement amplitude and (c) the pressure amplitude of the sound? Take the speed of sound to be 343 m/s and the density of air to be 1.21 kg/m? (a) Number i Units (6) Number Units (c) Number i Units