69. (a) We take the form of the displacement to be y(x, t) = ymsin(kx– ωt). The speed of a point on the cord isu(x, t) = ∂y/∂t= –ymcos(kx– t),and its maximum value is um= ym. The wave speed, on the other hand, is given by v= λ/T= /k. The ratio is 2./mmmmuyykyvkπ===λ(b) The ratio of the speeds depends only on the ratio of the amplitude to the wavelength.
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