Interference is a phenomenon characteristic for waves. When two waves meet, they interfere and result in a new wave. The precise shape of the resultant wave depends on the amplitude, frequency and phase of the constituent waves. In a most basic setting, two types of interference occur: constructive (resultant amplitude increases) and destructive (resultant amplitude decreases).
For this exercise we use the kinematics relations,
v² = v₀² + 2 a x
where v₀ is the initial velocity of the bullet, which as part of rest is zero, for the distance (x) we can assume that the gases accelerate along the entire trajectory of the cannon x = 2m