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## Homework Statement

Lets say a wire has Youngs modulus Y, Initial length L area A and is supporting some external load/force of magnitude F.......its extension is dl..We say that the Potential energy of wire is 1/2(YA/L)(dl

^{2}).....But i am having a problen with the energy changes.....

## Homework Equations

## The Attempt at a Solution

If its hanging down the work done by external force (gravity) is mgh....

So we want the potential energy of the wire....I was trying to derive it by using the external force.....Now work done by external force should be negative of work done by spring (from work energy theorem here change in KE is zero as initially and finally its at rest)....

So is 1/2(YA/L)(dl

^{2}) = mg*dl? IF so how?