Final answer:
The coin's acceleration when tossed upwards is always -9.80 m/s² due to the constant acceleration of gravity, regardless of its direction of motion.
Step-by-step explanation:
When a coin is tossed straight up into the air, its acceleration while moving upward after being released is not positive or initially positive. Instead, the acceleration is always in the opposite direction to its motion; it is negative since we've taken up as the positive direction. This is because the coin is under the influence of gravity, which imparts a constant acceleration of approximately -9.80 m/s², regardless of whether the coin is moving upward or downward. At the highest point in its trajectory, the coin's velocity will be zero, but the acceleration due to gravity will still be -9.80 m/s². Therefore, the acceleration of the coin is constant and equals the acceleration due to gravity throughout its entire flight from the moment it leaves the hand until it hits the ground.