The two helical springs with stiffness constant K1 and K2 are connected in series. What will be the combined stiffness K of this assembly of the springs?
1
\(\frac{1}{K}=K_1+K_2\)
2
\(K=\frac{K_1K_2}{K_1+K_2}\)
3
\(K=\frac{1}{K_1}+\frac{1}{K_2}\)
4
K = K1 + K2