Aslingshot is used to launch a stone horizontally from the top of a 20.0 meter cliff. the stone lands 36.0 meters away. at what speed was the stone launched ?

S= 1/2 x  a  x  t^2
time taken to drop down t =  √2s/a =  √(2(20)/9.8) = 2.02 seconds

time taken to travel horizontally 36 meters = 2.02 s
velocity = s/t = 36/2.02 = 17.8 m/s