when to put mg=kx and mgx=1/kx2 in spring mass system why in some places the eq.is mg=kx{k=spring constant} and sometimes it is mgx=1/2kx2

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Q. Dear Sir/Madam
I am unable to understand in questions, when to equate the forces and when to equate the work done by the respective forces in similar conditions.
Example: An object of mass m is suspended with an unstretched vertical spring. Whem mass m is just released after connecting to the spring, what is the masimum elongation of the spring?
In this question,
1. If I equate the net 'forces' acting on the mass after the total elongation i.e. mg= kx, I get x=mg/k
2. However if I equate the work done by gravitation force and spring force i.e. mgx=1/2kx^2, I get x = 2mg/x which is the answer.
Kindly help me understand when to equate forces and work done in such questions?

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