Answer:
Once the ball is place at the position A and then released, It will accelerate towards the mean position under its weight. At the mean piston it again maximum velocity and momentum so its moves up-to the position B due to inertia. At B it has zero velocity so zero kinetic energy but maximum potential energy.
Again from point B it will move towards O under the restoring Force having maximum velocity at O but does not stop at O due to inertia and will go up to A. In this way the ball will continue to oscillate between the points A and B about the point O, it has simple harmonic motion.
Step-by-step explanation: