Answers

2016-01-11T22:35:24+05:30
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PE of an object of mass m kept at a height h is mgh. 
Actually, the work done to lift this object against gravity to take it to a height h is stored (converted) as PE of this object. 

The work done = Force*distance 
=Mass*acceleration*distance 
=m*g*h 
=mgh 

therefore, PE=mgh
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2016-01-12T12:14:21+05:30
Work=force ×displacement
in vertical direction force is gravitational force vertically downward i.e. mg
let the displacement be h
so work done (potential energy)=mgh
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