Final answer:
The change in momentum of the ball when its momentum changes from P to minus P is -2P, representing a reversal and doubling of the momentum magnitude.
Step-by-step explanation:
The question involves a scenario where a ball changes its momentum from P to minus P after hitting off a bat. In Physics, momentum is a measure of the quantity of motion an object has, which is a product of mass and velocity. To calculate the change in momentum (ΔP), we subtract the final momentum from the initial momentum. Since the final momentum is -P and the initial momentum is P, the change in momentum is:
ΔP = Pfinal - Pinitial = -P - P = -2P.
The change in momentum of the ball is therefore -2P. This indicates that not only has the ball reversed its direction, but the magnitude of its momentum has also been doubled as a direct result of the collision with the bat.