Average acceleration is defined as:

.

In words, this definition indicates that the acceleration is equal to the rate at which the velocity is changing. Since is a positive scalar, the two vectors in the definition, and , have the same direction.

Point D is a turning point, hence the velocity of the ball at point D is zero. Consider a small portion of the motion with an initial point at point D and a final point just after point D. Since the velocity at point D is zero,

=

You indicated that the direction of the acceleration at point D is 8. Since and have the same direction, and since , this means that the final velocity of the ball (i.e., the velocity just after point D) is also in direction 8. Is the ball really moving in direction 8 just after point D?