Answer:
F=-3N
Explanation:
Newton's 2nd law
Fnet = ∆p/t
where ∆p = mv - mu (change in momentum or impluse).
So (assuming the ball continues to move in same direction).
∆p = 0.3kg*4.2m/s -0.3kg*4.5m/s
∆p= 1.26 N -1.35 N
∆p = -0.09 Ns
Therefore Fnet
Fnet=∆p/t
Fnet= -0.09N/0.030s
Fnet = -3N