A ball is thrown vertically upward from the surface of the earth. The ball rises to some maximum height and falls back toward the surface of the earth. Which one of the following statements concerning this situation is true if air resistance is neglected?
A)As the ball rises, its acceleration vector points upward.
B)The ball is a freely falling body for the duration of its flight.
C)The acceleration of the ball is zero when the ball is at its highest point.
D)The speed of the ball is negative while the ball falls back toward the earth.
E)The velocity and acceleration of the ball always point in the same direction.

Question

Quizplus · Accepted Answer

When air resistance is neglected, the only force acting on the ball throughout its flight is gravity. Therefore, the ball is in free fall for the entire duration of its flight, both when ascending and when descending. Choice A is incorrect because the acceleration vector of the ball initially points upward, but as the ball goes higher, the acceleration vector points downward due to the influence of gravity. Choice C is incorrect because the acceleration of the ball is always downward, even when the ball reaches its highest point. Choice D is incorrect because the speed of the ball, which is the magnitude of its velocity vector, is always positive, both when rising and when falling. Finally, choice E is incorrect because the velocity and acceleration vectors of the ball are in opposite directions during the entire flight (upward for velocity, downward for acceleration).

A Ball Is Thrown Vertically Upward from the Surface of the Earth