A cannon fires a cannon ball eastwards at a speed of 20 m/s (this speed is along the barrel of the cannon) and an angle of 45o above the horizontal. At the same time and from the exact same starting position a motorized cart begins to travel horizontally eastwards along the level ground. The cart, starting from rest, undergoes constant acceleration while the cannon ball rises and then moves with zero acceleration as the cannon ball falls back to the ground. Gravity act along the vertical at exactly -10 m/s2.
If the cart is to be at the same position as the cannon ball when the cannon lands, then what is the acceleration of the cart?