A sinusoidal wave travels along a long string in the positive x-direction. The figure shows the shape of the string at the instant $t = 0$: $y = A\sin kx$. The wave speed is $v = \omega/k$. Which graph shows the transverse velocity $v_y$ of the particles of the string against $x$ at this same instant?

Fig. 1: The shape of a string at t = 0, y = A sin kx, over two wavelengths, with an arrow showing the wave moving in the positive x-direction.

Graph (a)Graph (b)Graph (c)Graph (d)