Halliday, Resnick & Walker — Waves-I: Problem 26

26 If a transmission line in a cold climate collects ice, the increased diameter tends to cause vortex formation in a passing wind. The air pressure variations in the vortexes tend to cause the line to oscillate (gallop), especially if the frequency of the variations matches a resonant frequency of the line. In long lines, the resonant frequencies are so close that almost any wind speed can set up a resonant mode vigorous enough to pull down support towers or cause the line to short out with an adjacent line. If a transmission line has a length of 310 m, a linear density of 3.35 kg/m, and a tension of 90.1 MN, what are (a) the frequency of the fundamental mode and (b) the frequency difference between successive modes?