A stone is dropped at t = 0. A second stone, with twice the mass of the first, is dropped from the same point at t = 150 ms.

A stone is dropped at t = 0. A second stone, with twice the mass of the first, is dropped from the same point at t = 150 ms. (a) How far below the release point is the center of mass of the two stones at t = 550 ms? (Neither stone has yet reached the ground.) (b) How fast is the center of mass of the two-stone system moving at that time?