1. The problem statement, all variables and given/known data A rock is thrown downward from an unknown height above the ground with an initial speed of 27 m/s. It strikes the ground 7.1 s later. Determine the initial height of the rock above the ground. The acceleration of gravity is 9.8 m/s2. Answer in units of m. 2. Relevant equations [itex]\Delta[/itex]x = vit + 1/2 at2 3. The attempt at a solution I'm not sure if this equation is correct, first of all, but it has all of the variables given in the problem. I don't know how to deal with the fact that it's thrown down, but I thought the vi would take care of it. We have acceleration, initial velocity, and time, and the equation solves for displacement. What am I doing wrong? How should this problem be set up differently and why? Thank you very much.