Dependence of extention on length

[Brilli]

Homework Statement

A light uniform spring is tied between the ceiling and the floor keeping the spring vertical as shown in the figure. A bead of finite mass is glued at a distance l from the upper end and then allowed to go slowly down. The bead shifts a distance y.How does the y depend on l?

The Attempt at a Solution

I put that k(change in length of the spring upper part) +k ( change in legth of the lower part)=mg
And that both changes are same thus the changes in legth =(mgk)/2. But the answer says its wrong.
[/B]

 

[Orodruin]

The spring constant of a partial spring is not the same as the spring constant of the full spring.

 

[Brilli]

The spring constant of a partial spring is not the same as the spring constant of the full spring.

Thanks you so much!