1. The problem statement, all variables and given/known data A student throws a set of keys vertically upward to her sorority sister, who is in a window 2.00 m above. The second student catches the keys 2.30 s later. (a) What was the velocity of the keys just before they were caught? I did y(t) = 2 - 4.9t² + v₀t 2 = 0 - 4.9(2.3)² + v₀(2.3) v₀ = 12.1m/s Now I have two formulas, v² = v₀² + 2ad and v = v₀ + at, but they give me different answers. v² = v₀² + 2ad v² = (12.1)² + 2(-9.8)(2) v² = 107.21 v = 10.4m/s v = v₀ + at v = 12.1 - 9.8(2.3) v = -10.4m/s I understand the square root will give us a negative as well, but the question is, HOW DO WE KNOW which to take? I hadn't use the v = v₀ + at, I wouldn't know whether to take positive or negative.