Your friend is at the top of a building which you know to be exactly 100 feet high. She throws a stone downward at a speed V ft/sec, and you time how long it takes to hit the ground. The distance (in feet) fallen by the stone in t seconds is given by the formula s = 16t2 + v t. (No air resistance.) You time 2 seconds for the stone to fall to the ground. Using the above formula you can calculate the downward speed which is 18 ft/sec (check it by yourself). However you know your stopwatch is accurate only to within +0.1 sec. Use a tangent line approximation to infer an error estimate for the downward speed your friend threw the stone.