AP Physics problem with height, velocity, acceleration, and force of friction!?

Question

An object mass m dropped from a height h is moving at a velocity v just before ot hits the ground. If the acceleration of gravity is g, the average friction force acting on the object is...

Note: the answer is (2mgh-mv^2)/2h. I just need to know how to get there :-]]

Answer 1

From energy considerations.
Please note that the potential energy before the drop of this object: mgh
After drop but right before the object touches the ground: 0.5mv^2
The lose of the energy is due to friction force F through this fall (distance h), and the work done by this force is Fh:
Fh = mgh - 0.5mv^2
You get the result after rearrange this equation.