Finding the Max Extension of a Spring

[rgujju]

Problem
An ideal spring with spring constant 'k' is hung from the ceiling and a block of mass 'M' is attached to its lower end. The mass is released with the spring initially unstretched. Then the maximum extension in the spring is?

Please tell how to do it and the final answer.

 

[CAF123]

Consider energy conservation.

 

[rgujju]

I tried but i am not getting the right answer..

 

[voko]

Show what you have tried. You are required to by the rules of the forum.