Given that,
Mass of the ball, m = 0.025 kg
Initial speed, u = 4 m/s
To find,
Impulse when (a) the ground is soft and the ball stops dead
(b) the ground is hard and the ball bounces straight back at 2.0 m/s.
Solution,
Impulse = change in momentum
J = m(v-u)
(a) u = 0 (as it stops)
J = 0.025(4-0)
J = 0.1 N-m
(b) v = 2 m/s
J = 0.025(4-2)
= 0.05 N-m
Therefore, this is the required solution.