Answer
The frequency should be $0.0455~s^{-1}$
Work Step by Step
To simulate Earth's gravity, the radial acceleration should be equal to $g$. We can find the required angular velocity:
$\omega^2~r = g$
$\omega = \sqrt{\frac{g}{r}}$
$\omega = \sqrt{\frac{9.80~m/s^2}{120~m}}$
$\omega = 0.2858~rad/s$
We can find the frequency:
$f = \frac{\omega}{2\pi}$
$f = \frac{0.2858~rad/s}{2\pi}$
$f = 0.0455~s^{-1}$
The frequency should be $0.0455~s^{-1}$.
