Halliday, Resnick & Walker — Waves–I: Problem Problem_7

A sinusoidal wave is sent along a cord under tension, transporting energy at the average rate of \( P_{avg,1} \). Two waves, identical to that first one, are then to be sent along the cord with a phase difference \( \phi \) of either 0, 0.2 wavelength, or 0.5 wavelength. (a) With only mental calculation, rank those choices of \( \phi \) according to the average rate at which the waves will transport energy, greatest first. (b) For the first choice of \( \phi \), what is the average rate in terms of \( P_{avg,1} \)?