Answer
$\omega = 310~s^{-1}$
Work Step by Step
We can write a general expression for the standing wave:
$y'(x,t) = [(2y_m) sin ~(kx)]~cos~\omega t$
In part (b), we found that $~~k = 3.1~m^{-1}$
We can find $\omega$:
$\frac{\omega}{k} = v$
$\omega = v~k$
$\omega = (100~m/s)(3.1~m^{-1})$
$\omega = 310~s^{-1}$
