Answer:
The average net force on the ball is 1020 N.
Step-by-step explanation:
Given that,
Mass of the ball, m = 2 kg
Its initial speed, u = 30 m/s
Just after rebounding upward its speed is 21 m/s, v = -21 m/s (direction is opposite of the initial direction)
If this change in velocity took place in a time of 0.10 seconds, t = 0.1 s
We need to find the net force on the ball. The net force is given by the product of mass and its acceleration as:

a is acceleration of the ball

So, the average net force on the ball is 1020 N. Hence, this is the required solution.