Here's why:
* Gravity: The primary force acting on a projectile is gravity, which pulls it downwards. This causes the vertical velocity to decrease as the projectile rises.
* Apex: At the highest point of its path (the apex), the projectile momentarily stops moving upwards. This is the point where its vertical velocity becomes zero.
* Horizontal Motion: Since there's no force acting on the projectile horizontally (neglecting air resistance), its horizontal velocity remains constant throughout its flight.
Therefore, the speed of a projectile at the top of its trajectory is equal to its horizontal velocity.
