A boy is standing on the roof of his house, 10 m above the ground.

Question

A boy is standing on the roof of his house, 10 m above the ground. He sees his mean neighbor walking down the street, 20 m away, and decides to hit him with a water balloon. ​How fast must he throw the balloon?

Answer 1

Well if he throws the balloon horizontally with speed x.

Using s = ut + 0.5 a t²

with s = 10, u = 0, a = 9.81, the balloon will hit the ground in 1.43 s

It needs to travel horizontally 20m in that time, so x = 20 / 1.43 = 14 m/s

This assumes that the mean neighbour doesnt move during those 1.43 s !