1. The problem statement, all variables and given/known data A stone is thrown from a rooftop at time t = 0 seconds. Its position at time t is given by r(t) = 10ti - 5tj - (6.4 - 4.9t^2)k: The origin is at the base of the building, which is standing on at ground. Distance is measured in meters. The vector i points east, and k points up. At what time does the stone hits the ground? 2. Relevant equations 3. The attempt at a solution I am pretty sure that I need to find the height when the stone reaches the top.. am I right?