1. The problem statement, all variables and given/known data If a ball is thrown vertically upward with a velocity of 80 ft/sec, then its height after t seconds is given by s = 80t - 16t2 . What is the velocity of the ball when it is 96 feet above the ground on its way up? 2. Relevant equations 3. The attempt at a solution I have found my way to s'(t) = -16h -32t + 80 which I believe to be right. But now I'm not sure what to do. Do I need to find the second derivative?