9. a baseball is traveling (+20 m/s) and is hit by a bat. it leaves the bat traveling (-30 m/s). what is the change in the velocity? remember that direction is what makes velocity different than speed.

-50 m/s

Explanation:

In order to correctly calculate the change in velocity, we have to define a positive direction. Let's take the initial direction of the ball as positive direction.

This means that the initial velocity of the ball is:

while the final velocity of the ball will be negative:

Therefore, the change in velocity will be:

d is the correct answer