You indicated that the acceleration at point D is perpendicular to the velocity. 

If the angle between the ball’s velocity and acceleration is 90°, then the ball is turning but is neither speeding up nor slowing down.  Is this true? 

In addition, remember that at point D the ball is flying through a vacuum.  Hence, the acceleration of the ball at point D is the freefall acceleration (i.e., the acceleration of gravity).  In what direction is the freefall acceleration?

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