At the top of a parabolic trajectory, only two forces acting on the ball are its weight (W) and the normal force (N) which are equal in magnitude and opposite in direction, resulting in a net force of zero.
At the top of a parabolic trajectory, the ball is not accelerating vertically, so the net force acting on it in the vertical direction is zero which means that the weight of the ball (W) is equal to the normal force (N).
The weight of the ball (W) can be calculated using the formula
Weight = mg, where m = the mass of the ball (2 kg)
g = acceleration due to gravity (9.81 m/s²).
W = 2 kg × 9.81 m/s²
= 19.62 N
The weight of the ball is equal to the normal force (N), then N = 19.62 N.