Question

A ball of mass m is hung from the end of a vertical, unstretched spring of negligible mass and force constant k, then released from rest. After it has fallen a vertical distance l it is momentarily at rest again. What is l in terms of m, g, and k?.

Answer 1

PE = m g I change in potential energy of object

PE = 1/2 k I^2 change in potential energy of spring

m g I = 1/2 k I^2

I = 2 m g / k