The stationary wave produced on a string is represented by the equation $y=5 \cos \left(\frac{\pi x}{3}\right) \sin (40 \pi t)$ where $x$ and $y$ are in $\mathrm{cm}$ and $t$ is in seconds. The distance between consecutive nodes is
(a) $5 \mathrm{~cm}$
(b) $\pi \mathrm{cm}$
(c) $3 \mathrm{~cm}$
(d) $40 \mathrm{~cm}$