Here's why:
* Gravity: The only force acting on a projectile (ignoring air resistance) is gravity. This force pulls the projectile downwards, causing it to accelerate downwards throughout its entire flight.
* Velocity: At the top of its trajectory, the projectile's vertical velocity is zero. However, its horizontal velocity remains constant.
* Acceleration: Acceleration is the rate of change of velocity. Even though the vertical velocity is zero at the top, the projectile is still being accelerated downwards by gravity.
Therefore, the acceleration of a projectile at the top of its trajectory is equal to the acceleration due to gravity (approximately 9.8 m/s² downwards).
