Final answer:
At the top of its trajectory, the velocity of a ball thrown straight upward is zero, but acceleration due to gravity remains a constant -9.81 m/s², which means the acceleration is not zero.
Step-by-step explanation:
A ball thrown straight upward has its velocity momentarily become zero at the peak of its flight. However, this does not mean that the ball's acceleration is zero at that point. According to the laws of physics, specifically Newton's laws of motion, objects under the influence of gravity experience a constant acceleration due to gravity, which is approximately 9.81 m/s² downward near the Earth's surface. Thus, even though the velocity is zero at the top of its trajectory, the ball continues to experience acceleration.
When analyzing the motion of the ball, it is essential to understand that velocity and acceleration are two different quantities. Velocity is the speed of the ball in a given direction, while acceleration is the rate of change of velocity. An object thrown straight up will have its velocity decrease as it rises until it reaches zero at its highest point. Even though the velocity is zero at the peak, the ball is still under the influence of gravity, which imparts a constant acceleration directed downward throughout the motion. As soon as the ball starts descending, its velocity increases in the downward direction.
Therefore, at the peak of its trajectory, the ball's acceleration due to gravity is not zero but remains constant at approximately -9.81 m/s², with the negative sign indicating that the acceleration is in the opposite direction to the initial upward throw.