[EDITED. Thanks to Doc Al, Tanya Sharma and dauto] 1. The problem statement, all variables and given/known data A ball is dropped from rest from the top of a building of height h. At the same instant, a second ball is projected vertically upward from ground level, such that it has zero speed when it reaches the top of the building. (A) At the time when the two balls pass each other - which ball has the greater speed, or do they have the same speed? (B) Where will the two balls be when they are alongside each other: at height h/2 above the ground, below this height, or above this height? 2. Relevant equations Equations of 1D motion for a constant acceleration of -g 3. The attempt at a solution First here is the diagram I drew: Now for part (A): I suppose that the second ball was thrown up with velocity v0 And the balls pass each other at time t So for the first ball v = -gt And for the second ball v = v0 -gt So speed of the first ball |-gt| Speed of the second ball |v0 -gt| Now which one is greater? How can I tell?? I shall post my attempt for second part later but someone please help me deal with this. Thanks in advance!