Problem 36.

A ball is thrown upward with initial velocity v.  What is the change in speed on the way up? What is the change in speed on the way down? Disregard air resistance.

Solution:

The speed of the ball is the magnitude of velocity.

On the way up: initial speed is v, the final speed is 0. Then the change of the speed is 0-v=-v (it is negative).

On the way down: initial speed is 0, the final speed is v. Then the change of the speed is v-0=v (it is positive).