Question

Ball A is dropped from rest from a building of height H exactly as ball B is thrown up vertically from the ground. When they collide A has twice the speed of B. If the collision occurs at height h, what is h/H? Hint: Write equations for heights yA,yB and velocities vA,vB. What can you say about them at the time of the collision?

Answer 1

h/H=2/3 is the correct answer. Wondering if when h = 0 counts. Because it is speed not velocity. so is that possible that a and b collide when b is going down instead of going up. Thanks

Answer 2

The answer says we have made the reasonable assumption that the collision occurs while ball B is moving upward. Just do not understand why b cannot be going down