The figure below shows two springs connected in parallel. This combination can be thought of as being equivalent to a single spring having an effective force constant keff. Obviously, the effective force constant must be related to the force constants k1 and k2 of the individual springs. We will assume that the springs have no significant mass. Suppose we stretch the combination a total distance x from its equilibrium position.(Figure 1)

Question

If you connect a spring of force constant 35.0N/cm in parallel with one of force constant 55.0N/cm , what is the force constant of the single spring that will be equivalent to this combination?

Answer 1

x₁=x₂=x
F=F₁+F₂
F/x= F₁/x +F₂/x =
F₁/x₁+F₂/x₂ =>
k=k₁+k₂= 35+55 = 90 N/m