please see the attached document 
i hope it helps.......................
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Law of conservation of energy states - Energy is neither be created nor be destroyed. It can only be transform in one form of energy to another form. The total amount of energy in the universe remains constant.

In the case of freely falling body - The force acts on freely falling body is acceleration due to gravity and equal to mg i.e. mass * gravity. Hence it is converted from gravity energy to potential energy by position or configuration I suppose
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