Final answer:
The acceleration of a boulder thrown upward and falling back down is consistently 9.80 m/s^2 downward, regardless of its movement up, at the highest point, or down.
Step-by-step explanation:
The acceleration of an object thrown straight upward, such as a boulder, is subject to gravity throughout its entire trajectory. This includes moving upward, being at the highest point, and moving downward. The magnitude of the acceleration due to gravity is 9.80 m/s2, and it always points downwards towards the center of the Earth.
(i) While the boulder is moving upward, the acceleration is 9.80 m/s2 downward. (ii) As the boulder moves downward, the acceleration remains the same in magnitude and direction, 9.80 m/s2 downward. (iii) At the highest point, although the velocity of the boulder is zero, the acceleration is still 9.80 m/s2 downward.