As you fall, your gravitational potential is transformed into kinetic energy.
Now assuming that there is no air resistance to transform any of the kinetic energy into thermal (heat) energy due to friction, your gravitational potential energy at the top will be equal to your kinetic energy at the bottom. This is because all of the energy will have been transferred.
You would get this equation:
But now we can cancel the mass:
Finally we can rearrange what is left to get an equation for the velocity v when you hit the ground:
Notice that v does not depend on the mass of the object, because that cancelled out. Hence all objects will hit the ground at the same speed if there is no air resistance.
