In this experiment, you will be using a ball rolling in a spherical cap. Consider a ball of radius r_b, in a spherical cap of radius r_s.  Imagine that you place the ball inside the spherical cap at some small distance from the center of the cap, and let go.  Draw a clearly labelled diagram of this situation to familiarise yourself with the forces.

We will model this experimental setup as a pendulum; ignoring friction. Which of the following then (for the situation described previously) is the appropriate equation for the period of oscillation of the ball?