Walker, Halliday & Resnick — Potential Energy and Conservation of Energy: Problem 19

19 A 1.0 kg block moving at 8.0 m/s strikes a spring fixed at one end to a wall and compresses the spring by 0.40 m, where its speed gets reduced to 2.0 m/s. After this event, the spring is mounted upright by fixing its bottom end to a floor, and a stone of mass 2.0 kg is placed on it; the spring is now compressed by 0.50 m from its rest length. The system is then released. How far above the rest-length point does the stone rise?