A ball is dropped from a treetop 256 feet above the ground. How long does it take to hit the ground?

Assuming gravity is constant and ignoring wind resistance ...

h (t) = hi+vit-16t^2 ... vi=0 and hi=256 so

h (t) = 256-16t^2

When it hits the ground, h=0 so

256-16t^2=0

16t^2=256

t^2=16, and since t>0

t=4 seconds