Simply the idea of this is shooting a big rubber ball out of a cannon. Now there is more to this, I have already got all the calculations for the cannon and trajectory fire points but the main issues is the ball itself.

The graph hopefully will help show the balls path given the angle of the cannon. What I am asking is, this ball will be rectangular at a later point, the ball has to bounce roughly 0.6x the previous height etc. Is it better to do this using unity's inbuilt physics engine, as I am creating a scrolling background treadmill effect and will need to constantly add forces to this object as it hits obstacles during its path. Or should I programatically implement my own gravity, acceleration, terminal velocity for more control over increasing both x and y axis velocity.

NOTE: This is for a 2D game and the ball can not roll backwards at any stage. I have implemented both methods but not entirely, I thought I would ask as I have sunk quite a lot of time into this so far and have a base working of each but each with their own flaws.