Answer the following with reference to linear momentum and its rate of change:
(i) Define linear momentum and state its SI unit.
(ii) Explain qualitatively how the momentum of a body changes when a constant unbalanced force acts on it.
(iii) A rubber ball of mass 0.20kg moving with speed 5ms−1 strikes a rigid wall and rebounds straight back with the same speed. Is the average force exerted by the wall on the ball during the impact zero? Give a reason based on the concept of rate of change of momentum.