Potential energy U for a system is defined as: Wint =−∆U=−(Uf−Ui)...(1)
f
∫
i
→
F
⋅
→
dr
=−(Uf−Ui)...(2) ⇒ Where
→
F
is an internal conservative force, and Wint is work done by the internal conservative force. ⇒ If U increases then Uf>Ui , or the term −(Uf−Ui) will be −ve . ⇒Wint will become −ve ∴ System has done work against the conservative force