Final answer:
The acceleration of a rock thrown straight upward remains constant at -9.80 m/s² downward throughout its journey—while going up, at the peak, and coming down.
Step-by-step explanation:
Understanding the Acceleration of a Thrown Rock
When a rock is thrown straight upward, the acceleration on the way up, at the top, and on the way down is affected by the force of gravity. During the upward motion, even as the rock slows down due to opposing gravity, its acceleration remains downward at a constant rate of approximately -9.80 m/s². At the top of its flight, where the velocity of the rock is zero, the acceleration is still downward at -9.80 m/s², because only the velocity has been neutralized, not the acceleration due to gravity. On the way down, the rock's acceleration remains constant at -9.80 m/s² downward, as gravity accelerates the rock back towards Earth. Thus, the correct answer is b) Downward; zero; upward.