Q:  What is the moment of inertia of the ball around its
      the point of contact with the ramp?


           In order to compute the moment of inertia around the
           point "P" -- the point of contact between ball and ramp --
           we need to use the parallel-axis theorem.



              I (around P)  =  I (around center)  +  M * (distance to P)^2

                            =   (2/3) M * R^2     +  M * R^2

                            =   (5/3) M * R^2