F = ke
k = F1e1
F1 = 10N, e1 = 0.02m
F2 = 40N, e2 = ?
F1e1 = F2e2
100.02 = 40e2
e2 = 40×0.0210 = 0.08m
The new length = 1 + 0.08 = 1.08m