If the bat were a stationary, large-mass object such as a wall, the rebounded baseball would travel away only about as fast as it came in. A pitched ball with a faster incoming speed would bounce away faster. A similar argument shows why a fast incoming baseball will rebound from a moving bat much faster than a slow incoming baseball.
Work Step by Step
This can be shown formally by applying equation 7–7 for a 1-D elastic collision. This is also similar to the “gravitational slingshot” effect discussed on page 197.