Answer
d
Work Step by Step
The initial speed of the ball $(-30m/s)$ is faster than terminal velocity $(-15m/s)$, which means that friction with the air is stronger than the force of gravity on the ball. This means the ball will slow down until it reaches terminal velocity.
The force or friction with the air is proportional to the speed of the ball, so the ball slows down at a decreasing rate, resulting in a curved velocity diagram starting with a steep slope eventually becoming flat at terminal velocity.
