as we know that when there is a free fall of an object,the decrease in potential energy at any point on its path,appears as an equal amount of increase in its kinetic energy ...because by the law of conservation of energy energy can neither be destroyed nor be created.
mechanical energy=kinetic +potential
potential energy at the top(maximum)=mgh
kinetic energy when it reaches the ground(maximum)=1/2mv^2
potential energy=kinetic energy (law of conservation of energy)
THE SPEED JUST BEFORE IT HITS THE GROUND IS-