Calculating trajectory of ball rolling down slope and off launch ramp
You seem to be a little off track.
The change in gravitional potential energy of the ball is
delta energy = delta height * mass * g
delta height is the difference between the starting position of the ball and the height of the exit ramp.
This energy is converted from potential energy to kinetic (movement) energy of the ball. This kenetic energy has 2 components - movement and rotation.