A light elastic string has natural length 2l and modulus of elasticity 4mg. One end of the string is attached to a fixed point A and the other end to a fixed point B, where A and B lie on a smooth horizontal tabel, with AB = 4l. A particle P of mass m is attached to the mid point of the string.

The particle is released from rest at the point of the line AB which is 5l/3 from B the speed of P at the mid-point AB is V

Find V in terms of gland L

Well... errr i dont have a clue :\ x = acoswt possibly differentiate to find speed, but the at the midpoint a = 0, so that wouldn't work :\ As we're told modulus im thinking EPE, but what is the extension. THe string has alreayd been extended from 2l to 4l when it was attached between A and B and now the particle P on it has been pulled towards B and has been let go. Sheeez. That's tricky.