1. The problem statement, all variables and given/known data You throw a small rock straight up from the edge of a highway bridge that crosses a river. The rock passes you on its way down, 5.00 s after it was thrown. What is the speed of the rock just before it reaches the water 21.0 m below the point where the rock left your hand? Ignore air resistance. 2. Relevant equations y= y0+v0t-1/2*gt2 v= v0 -1/2*gt. 3. The attempt at a solution I used v= v0 -1/2*gt to arrive at the velocity that the rock was going at the moment it was passing the hand. My answer was v= 0- 1/2*(9.8m/s2), which gave me 24.5m/s. I have an idea of where to go from here. I know I need to use v2 − 2g(y − y 0). My issue is that I don't want to just memorize the equation. I need help deriving it from the two basic equations: y= y0+v0t-1/2*gt2 and v= v0 -1/2*gt. Once I do that, I believe I can finish the problem on my own.