What is the Force Due to Extension for a Particle on an Elastic String?

[osy044]

Homework Statement

A particle of mass m is attached to one end of a light elastic string of natural length a and modulus mg, the other end of the sting is attached to a fixed point O on smooth horizontal surface. The particle is released from rest at horizontal distance a+L from O.

calculate the force due to extension of string.

Homework Equations

The Attempt at a Solution

obviously one of the force will be 'mg' but force due to extension is hard to calculate. the answer for that one is mgx/a.
Also I am not sure if that modulus means young modulus
PLEASE help me

 

[Delphi51]

The spring is stretched distance L. The force due to the stretch is
F = kL, where k is the spring constant.

The mgx/a answer you quote is unreasonable because it does not contain the amount of stretch, L, and does contain g which is not involved in a purely horizontal problem.

 

[osy044]

i thought so too. its seemingly unreasonable.