1. The problem statement, all variables and given/known data A boy standing on the top of a building 40m high throws a ball directly aiming to his friend standing on the ground 30m away from the base of the building. If the projection velocity is 20m/s. Find how short will the ball fall from his friend. 2. Relevant equations 3. The attempt at a solution From the picture I have attached, AB = 40 m BC = 30 m Using pythagoras theorem, we have AC = 50 m Using tan θ = p/b we have tan θ = 40/30 so, θ = tan-1(4/3) = 53° Now, breaking the components, Horizontally: 20 * cos53° = 16 m/s Vertically, 20 * sin 53° = 12m/s My problem begins here : 1) Which formula do I use, s = ut + 1/2 at2 or v = u + at to find the time it takes to reach ground vertically. 2) What's the sign of u and g here.