1. The problem statement, all variables and given/known data What is the effective spring constant for the system of the two springs, perfect pulley, and string shown on the left for it to be modeled by just one spring (constant keff) as shown on the right? 2. Relevant equations 3. The attempt at a solution With k2 getting stretched by D, the pulley goes down by 2D. Therefore, x1 = F/k1, x2 = F/k2 x1 + 2(x2) = F/k1 + 2F/k2 Solving this, I get k effective as (2*k1*k2)/(k2+2*k1) But this doesn't match the given answer. Where am I going wrong?