When a baseball is thrown straight upward, what is its acceleration at its greatest height?

a. 9.8 m/s2 upward
b. 9.8 m/s2 downward (my answer?)
c. 0 m/s2
d. 9.8 m/s2 horizontally

THE ENTIRE TIME the acceleration is one g, about 9.8 m/s^2 downward.

In other words yes, b

c. 0 m/s2

At the highest point of its trajectory, the baseball momentarily comes to a stop before starting to fall back downwards. This means that its velocity (and therefore acceleration) is zero at that moment. So, the correct answer is option c. 0 m/s2.

To determine the acceleration at the greatest height when a baseball is thrown straight upward, we need to consider the motion of the baseball during different phases.

When the baseball is thrown upward, it experiences a vertical acceleration due to gravity. At the highest point of its trajectory, the ball momentarily stops moving upward and starts to fall back down. This is where we need to determine the acceleration.

According to Newton's second law of motion, the acceleration of an object is equal to the net force acting on it divided by its mass. In this case, the net force acting on the ball is the force of gravity pulling it downward.

Therefore, the correct answer is b. 9.8 m/s² downward.

At the highest point of its trajectory, the ball's vertical acceleration is 9.8 m/s² in the downward direction, which is the acceleration due to gravity near the surface of the Earth.