Two balls of different mass are dropped from the top of a tall building one after the other. The distance between the balls

A.     increases with time.

B.     depends on the initial velocity only.

C.     remains constant.

D.     depends on the mass of the balls.

A

This is a common mind-teaser that very few students were able to answer correctly. At its heart is a clear understanding of the concept of acceleration. As the two balls have the same acceleration they will have a fixed velocity difference between them, meaning that the distance between them increases with time.