Final answer:
At its maximum height, the force on the ball is equal to its weight.
Step-by-step explanation:
The force on the ball at its maximum height, where its speed is instantaneously zero, is equal to its weight. When the ball reaches its highest point, it experiences a net force equal to the force of gravity pulling it downwards. This force is equal in magnitude and opposite in direction to the weight of the ball, resulting in a net force of zero on the ball.