What is the direction of an object's velocity and acceleration when a projectile is at the highest point of its trajectory?

At the highest point of a projectile's trajectory, the object's velocity is directed horizontally while the acceleration due to gravity is directed downward. This means that the two vectors—velocity and acceleration—are indeed perpendicular to each other.

As the projectile reaches its peak, it momentarily stops gaining height, resulting in a velocity of zero in the vertical direction. However, the horizontal component of velocity remains, assuming no air resistance is acting on it. In contrast, acceleration, which is influenced by gravity, continuously pulls the projectile downwards throughout its flight.

Choosing the option indicating that both are directed downward or upward would misinterpret the physics of projectile motion, as would suggesting that both vectors are directed horizontally. The fundamental concept here is that while the projectile travels horizontally at the highest point, gravity continues to exert a downward acceleration, leading to the perpendicular relationship between the two at that moment.