# Weightless roller coaster

A roller coaster goes over a hill of radius $30\text{ m}$. If the roller coaster moves at a great speed, then it will lose contact with the ground and fall freely in a parabolic trajectory. Under the free fall, people sitting in the roller coaster will feel weightless.

What is the minimum speed (in $\text{m/s}$) required to achieve the weightlessness?

Take $g = 9.8\text{ m/s}^{2}$.