A cannonball (mass =2 kg) is fired at a target of 500 m away. The 400 kg cannon recoils with a velocity of 2 m/s . Assuming cannon ball moves with constant velocity, when will it hit the target?
From the law of conservation of momentum, total momentum before firing = total momentum after firing. Therefore,
0 = mass of cannon × velocity of cannon + mass of cannonball × velocity of cannonball
0=400×(−2)+2×v
⇒v=400×22
=400 m/s
Hence, the velocity of the cannonball will be 400 m/s.
Thus, time taken to hit the target = 500400=1.25 s