Ignoring air resistance, what is true about the vertical motion of a fastball as it travels upward and then downward?

• A. The vertical speed stays constant.
• B. The vertical speed increases upward due to gravity.
• C. The vertical speed increases downward due to gravity.
• D. The vertical speed decreases downward due to gravity.

Answer: (C)

Gravity provides a constant downward acceleration, so the vertical component of the ball’s velocity changes as it moves. As it rises, the upward velocity is slowed by gravity, eventually reaching zero at the top. Once it starts to fall, gravity continues to pull downward, causing the downward speed to increase as it descends. That’s why the vertical speed increases downward due to gravity. The other statements don’t fit because gravity does not keep speed constant, does not increase upward speed while the ball is going up, and does not decrease downward speed as it falls.