Final answer:
Immediately after being thrown, a ball's vertical acceleration is 9.8 m/s² downward, due to Earth's gravitational pull, regardless of its horizontal movement.
Step-by-step explanation:
Just after a ball is thrown up at 30° above the horizontal, its acceleration is 9.8 m/s² downwards, due to Earth's gravity. The scenario implies that, in the absence of air friction, the only force acting on the ball after it is released is gravity, which accelerates all objects downwards at a constant rate regardless of their horizontal motion. Whether the ball is thrown upwards, downwards, or at an angle, as long as it is in the air and affected only by gravity, its vertical acceleration remains constant at approximately 9.8 m/s². The horizontal component of the ball's motion is unaccelerated because there is no horizontal force acting on it (assuming no air resistance).