Physics
posted by Lindsay .
A ball is thrown horizontally from a height of 16.01 m and hits the ground with a speed that is 5.0 times its initial speed. What was the initial speed?
This question really boggles my brain. I have no idea how to solve this, given only the height. Could someone please steer me in the right direction?

You can calculate the vertical final velocity from the height. Then, knowing the magnitude of speed, you can determine the horizontal speed.
5v=sqrt(vfvertical^2 + v^2)
square both sides, solve for v, the intial horizontal velocty. 
Ok makes sense. The only part I'm a little confused about is finding the horizontal speed...which equation is that?