# Illogical conclusion about a mass on a spring [closed]

If you place a weight on a spring and it is an equilibrium, then you have this equation:

$$mg = kx$$

you would solve for k and get:

$$k = mg/x$$

but, if we used conservation of energy, assuming that when the mass is on the spring it is at x = 0, we would get:

$$1/2kx^2 = mgx$$ we would get $$k = 2mg/x$$

What assumption am I making that is false? How would the k value be different with two correct statements?

• You need to include the kinetic energy of the mass. Dec 12, 2022 at 5:44
• Welcome to Physics! Please use MathJax to type equations and mathematical symbols. Dec 12, 2022 at 5:44
• @josephh Thanks a lot! I realized right when I submitted. That makes everything a lot clearer. Thanks for your help! Dec 12, 2022 at 6:02
• No worries at all. Dec 12, 2022 at 6:02
• Dec 12, 2022 at 6:14