In an experiment, a student launches a ball with an initial horizontal velocity at an elevation 2 meters above ground. The ball follows a parabolic trajectory until it hits the ground. Which of the following accurately describes the graph of the ball's vertical acceleration versus time (taking the downward direction to be negative)?
- A negative value that does not change with time
- A gradually increasing negative value (straight line)
- An increasing rate of negative values over time
- (parabolic curve)
- Zero at all times since the initial motion is horizontal