Referring to the rider man who tosses a ball from a motorcycle ahead of him the equation is no accurate because the inertia of the body the (ball) is not taking in consideration
even if the ball has little inertia it should be included in the equation.
For example . let the man the rider be sitting on a small wagon and they together make 100 pounds and let the ball be 100 pounds so they both have the same inertia; now lets give a tiny push let say with a velocity 5 feet second to the wagon and tell the man to trow the ball ahead of him
should the reduced speed of the wagon , be consider in the equation ; no need to know the velocity of the ball in this case.