At every point of the trajectory of the projectile, which of the following quantities is always zero?

Explanation

Projectile motion can be analyzed by breaking it down into horizontal and vertical components. In the absence of air resistance, the horizontal velocity of a projectile remains constant throughout its trajectory, and there is no horizontal acceleration. The vertical motion of a projectile is affected by gravity, so there is a constant vertical acceleration throughout the motion. However, at the highest point of the trajectory, the vertical velocity of the projectile becomes zero before changing direction and starting to move downward. Therefore, neither the vertical velocity nor the total velocity is always zero throughout the trajectory. Thus, the only quantity that is always zero throughout the projectile's trajectory is the horizontal acceleration.