1. The problem statement, all variables and given/known data A ball is thrown horizontally wit speed 20m/s, from the top of the building which is 30m high. Find the time the ball takes to reach the ground? 2. Relevant equations S= ut+0.5at^2 3. The attempt at a solution S=-30 u=0 A=9.8 T=? When I pluck the values I will get t^s=-30/4.9 but when we square root we will get complex number, but if I take the displacement as +30 then it will give me a positive value, so I am confused on why the s is not negative. If I say the displacement where the ball is on top of the building, then the displacement is 0 but if it goes down then it should be negative value.