Answer
$11.7cm$
Work Step by Step
We know that,
$v=f\lambda$
This can be rearranged as;
$\lambda=\frac{v}{f}$
We plug in the known values to obtain:
$\lambda=\frac{350}{500}=0.7m$
We also know that one cycle is equal to $2\pi$ radians. This means that $\frac{\pi}{3}$ refers to one sixth of a cycle.
Thus, the required length can be determined as
$\frac{\lambda}{6}=\frac{0.7}{6}=0.117m=11.7cm$
