Answer:
When we throw a projectile up, the negative gravity acceleration acts on it. Thus, when the ball reaches the highest point, the speed of the ball becomes zero.
Explanation:
Acceleration is a vector magnitude that indicates the variation of speed per unit of time.
As displacement, velocity and acceleration are vectors we will analyze this vectorly.
We consider positive acceleration when the acceleration vector is directed in the same direction as the movement. (Acceleration)
On the other hand, we consider negative acceleration when the acceleration vector is directed in the opposite direction to the movement. (de-acceleration)
