If the wire diameter of a compressive helical spring is

If the wire diameter of a compressive helical spring is increased by 2%, the change in spring stiffness (in%) is _______ (correct to two decimal places.)

Stiffness of helical spring

k =	Gd⁴
	64R³ n

∴ k ∝ d⁴

	k'	=		d'		⁴
	k			d

k' =		1.02 d		⁴	k
		d

k' = 1.08243 k

% increase in k =	k' - k	× 100%
	k

=		1.08243 k - k		× 100% = 8.243%
		k