Competency #1
Answer and Explanation
The correct answer is B.
An object in free fall has only 1 force acting on it in a significant way: gravity. Since there is only one force acting and this force is down, there must be a net force downward. A net force downward means there is an acceleration downward, by Newton's 2nd Law,
If the object is accelerating, it means the objects speed is constantly changing.
Choices A and D have equally spaced distances for at least some of the times shown. The equal spacing indicates constant velocity, which means the acceleration is zero for at least some portion of the run. Therefore, choices A and D cannot be correct.
Choices B and C both depict constantly accelerating balls. The ball in choice C is getting slower and slower with time, which indicates an upward acceleration in this case. The ball in choice B is getting faster and faster with time, representing a downward acceleration. We know from the above discussion that a ball in free fall accelerates downward, so choice B is the best answer.