# Young modulus question

1. Sep 6, 2010

### osy044

1. The problem statement, all variables and given/known data
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.

2. Relevant equations

3. 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 im not sure if that modulus means young modulus

2. Sep 8, 2010

### 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.

3. Sep 8, 2010

### osy044

i thought so too. its seemingly unreasonable.