Work Step by Step
Choice A is incorrect because the speed of the wave on the cord is constant, but the piece of cord moves at varying speed (and there is no general relationship between the wave speed and the top speed of the piece of cord, either). As the wave travels down the cord, a particular piece of the cord moves vertically between a low point and a high point. This piece of cord and the wave have the same amplitude. The piece of cord finishes a complete up and down cycle as one wavelength passes through. In other words, the piece of cord moves at the same frequency as the wave.