Final answer:
The acceleration of a coin tossed straight up is constant at -9.80 m/s², opposite to the direction of motion, for the entire duration of its flight.
Step-by-step explanation:
When you toss a coin straight up, it moves upward, turns around, and drops. During this entire motion, the acceleration of the coin is always in the same direction, which is downward due to gravity. This acceleration is constant and has a value of approximately -9.80 m/s² (negative indicates direction down toward the center of the Earth).
At the highest point, when the coin turns around, its velocity is momentarily zero, but the acceleration due to gravity remains constant and does not change to zero. Hence, the correct answer is that the acceleration is initially positive in the upward direction but remains consistently negative throughout the motion until it hits the ground.