(Moderator note: moved from technical forums, so no template) Does anyone know how to answer this question? A 1 meter spring lies horizontally on a table. You hang it vertically being held by one of its ends. Because of the mass of the spring itself it now extends to 1.1 meter. You hang a holder of unknown mass and now it's 1.2 meters long. You decide to hang a 500 gram mass on the holder and now, it's 1.3 meters long. What is the spring constant of the spring? I tried to use K = mgx, with m=0.5kg, g=9.81m/s2, and x=1.3-1.1m but the answer was not correct. Thanks!