Two springs have their force constant as k1 and k2 (k1>k2). When they are stretched by the same force up to equilibrium:
(3)
F1=F2
∵ w1=12k1x12, k1x1=k2x2=F
w1=12k1[Fk1]2=12F2k1
∴ w2=12F2k2
∵ k1>k2
∴ w1<w2