Final answer:
The horizontal velocity of a projectile remains constant, as there is no horizontal acceleration, while the vertical velocity changes due to gravitational acceleration. At the peak of its arc, the vertical velocity is zero before increasing again in the opposite direction during descent.
Step-by-step explanation:
The motion of a projectile can be described by analyzing its components in the horizontal and vertical directions, which are independent of each other. In the horizontal direction, acceleration (ax) is zero, thus the horizontal velocity (vx) remains constant throughout the projectile's flight. In contrast, the vertical velocity (vy) changes due to the acceleration caused by gravity (ay = -9.8 m/s2).
As a projectile moves upwards, its vertical velocity decreases until it reaches its peak, where vy is momentarily zero. When falling back down, the vertical velocity increases again in magnitude but in the opposite direction. Throughout this motion, the horizontal component of the velocity remains unaffected by gravity and does not change.
Therefore, we can analyze projectile motion as two separate one-dimensional motions: a constant velocity in the horizontal direction (due to no horizontal acceleration) and a uniformly accelerated motion in the vertical direction (due to gravity).