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?

2 answers

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?