Here is the question I am trying to awnser: A ball is thrown straight up and reaches a maximum height in 6.81 s. What was the ball's initial speed? Keeping in mind that we are not yet dealing with any sort of friction... So for problems like this I do the following: Given: Xo - 0 X - ? (this might be zero I'm not sure) Vo - ? V - ? (this might be zero I'm not sure) a - 9.8 m/s t - 6.81 at it's maximum height I need to solve for Vo. I'm not sure how to do this though. I know I should use one of the equations of: http://webphysics.iupui.edu/152/152F04/152Basics/kinematics/gif/kineq01.gif [Broken] But I have no idea beyond that... I tried the V=Vo + at with V as zero and t as 13.62 seconds (I doubled it beacuse I thought I should in order to get the complete time) and when I did that I got Vo as a negative... And I know it's not a negative... Any help???