a rock is directly thrown upward from the edge of a roof of a building that is 56.3m tall. the rock misses the building on its way down, and is observed to strike the ground 4 seconds after being thrown. with what speed was the rock thrown?

Answer 1

hf=hi+vi*t-4.9t^2
hf=0, hi=56.3, t=4.0
solve for vi