Past exam of the physics course of the year 1 of the natural sciences course of the University of Cambridge / 2024 / Paper 1 / Section B / 6 / e

Let $x=0.400\mathrm{m}$ be the compression and $m_t=0.550\mathrm{kg}$ the combined mass. Starting from rest at the top, it falls through $H+x$ before maximum compression. HenceThe gravitational drop during compression must be included. Equating $kx$ to the weight would instead describe a static equilibrium, not the turning point after a fall.