Final answer:
The correct answer is C) Horizontal. The horizontal component of the cannonball's velocity remains constant in projectile motion, whereas the vertical component changes due to gravity.
Step-by-step explanation:
The component of a cannonball's velocity that is parallel to the ground when it is in projectile motion is the horizontal component. This is one of the two independent components of motion in projectile dynamics; the other is the vertical component, which is influenced by gravity. In projectile motion, there is no horizontal acceleration if we ignore air resistance, meaning the horizontal velocity remains constant throughout the motion. However, the vertical velocity changes due to the acceleration caused by gravity, which is 9.8 m/s2 downwards.
Example: Considering the cannonball is launched horizontally, the initial vertical velocity is zero, and only the horizontal velocity needs to be computed. Using this principle, if a ball is thrown horizontally from a height, it will have zero initial vertical velocity, and its acceleration will be purely due to gravity; meanwhile, its horizontal velocity will remain constant until impact with the ground.