I need some clarification on this question
A light elastic string of natural length 50 cm and modulus 20 N has one end fastened to O on a smooth horizontal table. The other end has a particle of mass 0.4 kg attached to it and the particle is released from rest at a distance 60 cm from O. Find the time it takes to reach O.
The Attempt at a Solution
While the string is stretched
So,a = -100x
I get stuck from here. Can anyone help please? Thanks