Final answer:
The increase in energy and mass of a thrown ball, according to the Theory of Relativity, comes from the ball's velocity, as mass and energy are equivalent and interchangeable.
Step-by-step explanation:
According to the Theory of Relativity (E = mc²), the increase in energy and mass to a ball that has been thrown comes from the ball's velocity. When an object moves with a high velocity, its relativistic kinetic energy increases, and this increase in energy correlates to an increase in mass according to the equation E = mc², famously derived from the theory of special relativity. This is because energy and mass are equivalent, as mass can be converted to energy and vice versa. While we typically do not notice the increase in mass for everyday velocities because the change is extremely small, it becomes significant at speeds approaching the speed of light.