1. The problem statement, all variables and given/known data "A spring is hung from the ceiling. A pan of mass 100.0 g is attached to the end, which causes it to stretch 5.00 cm. Find the maximum distance the pan moves downward when a lump of clay of mass 120.0 g is dropped from a height of 40.0 cm onto the pan." The correct answer, according to my teacher is 0.233 meters. 2. Relevant equations Conservation of momentum, perfectly inelastic collision. m1v1i + m2v2i = (m1 + m2)vf Conservation of mechanical energy. MEi = MEf PEg = mgh PEe = 1/2 kx^2 KE = 1/2 mv^2 Work kinetic energy theorem. Fnet d cosθ = 1/2 m (vf^2 - vi^2) 3. The attempt at a solution I tried a perfectly inelastic conservation of momentum + work-KE theorem approach. m(ball)v0 + 0 = M(combined)v(final) Fnet d cos(θ) = 1/2 M(vf^2 - vi^2) where Fnet was the average spring force minus gravity, F = [k(0.05) + k(x)] / 2 - M(combined)g d was (x+0.05) and vf = 0, vi = root(2gh) UPDATE: OK so I tried conservation of mechanical energy after the collision to no avail. I did: 1/2 (.22kg) (1.53 m/s)^2 + (.22 kg)(9.81) x = 1/2 (19.62 N/m) (x+0.05)^2 Solving for x I got x = 0.225 m. I still can't get x = 0.233m. I'm sure it's not a rounding error of some sort. What am I missing?