Let a pring with force constant k is compressed by x1. Stored potential energy of the spring U1 = 12 k x2 . Let it be further compressed by x2. Let it be further compressed by x2 . Change in potential energy of the spring
k [ (() - )]
ΔU = Uf - Ui
Uf=12K(x1+x2)2
Ui = 12K x12
∴ Δ U= 12 K (x1+x2)2 - 12 k x12