Final answer:
The ball's initial acceleration when shot straight up is -1 times the gravitational acceleration g, that is, -9.8 m/s², which represents deceleration due to gravity.
Step-by-step explanation:
The magnitude of a ball's initial acceleration when shot straight up is, in fact, the same as the acceleration due to gravity, but in the opposite direction since gravity slows the ascent down. Considering that we've defined the upward direction as positive in our analysis, the initial acceleration would be -g or -9.8 m/s². So, if we were to express the ball's initial acceleration as a multiple of g, it would be -1 times g, indicating that the ball is decelerating at a rate equivalent to the acceleration due to gravity. However, it's important to note that an object in free fall or thrown upwards only has the gravitational acceleration g acting on it once it is released. Before that point, when being propelled upwards, other forces are at play to initiate the ascent.