Compression of a spring. Hooke’s Law vs. Conservation of Energy

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

Lets say I have a spring with a stiffness of k = 250 N/m originally unstretched. I then gently place a 5 kg block on top of the spring. How much does the spring compress?

2. Relevant equations

W = mg
F = -ks
mgΔh = 0.5k(Δh)2

3. The attempt at a solution

Using Hooke’s Law I get the following result

W = 5*9.81 = 49.05 N

W = F = -kx

49.05 = 250x meaning x = 0.1962 m

Using conservation of energy I get this though:

mgx = 0.5kx2

0 = 125x2 – 49.05x

x = 0.3924 m

So which one is the correct answer? Why is one double the other?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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