Final answer:
The magnitude of the initial velocity of the baseball is 71.33 m/s.
Step-by-step explanation:
The magnitude of the initial velocity of the baseball can be found by considering the change in velocity during the collision.
Given that the baseball's initial velocity is 80 mi/h in the -x-direction and it ends up moving 80 mi/h in the +x-direction after the collision, we can deduce that the change in velocity is 160 mi/h.
Since velocity is a vector, we need to convert the units to m/s and then find the magnitude of this change by taking the absolute value. Therefore, the magnitude of the initial velocity of the baseball is 71.33 m/s.