when an object is dropped from a certain height, it is a freefall. when in freefall, the only external force acting on the body is gravitational force (neglecting air resistance). the motion of the object is unformly accelerated motion:
(v2)^2 - (v1)^2 = 2*g*h
where
v2 = final velocity
v1 = initial velocity
h = height or distance traveled
g = acceleration due to gravity (9.8 m/s^2)
solving for velocity:
v2 = sqrt[ 2gh - (v1)^2 ]
when the object starts from rest (and thus v1 = 0),
v2 = sqrt(2gh)