1. The problem statement, all variables and given/known data A mass of 6.40 kg is hung from a spring with aforce constant of 7.80*10^3 N/m. The spring unstretched is 0.120m long. Find the distance that the spring stretches. 2. Relevant equations F = k*x is the way that gives the answer in my textbook. I tried W = 0.5*k*x^2. 3. The attempt at a solution What is wrong with the following? I used W = 0.5*k*x^2 = 0.5*7800N/m*x^2 . Then made W = m*g*x. So, m*g*x = 0.5*7800N/m*x^2. Then I cancelled out the x from both sides, and isolate the remaining x, so x = (m*g)/(0.5*78000N/m) = 0.136m. My answer is close to the correct answer of x = 0.128m, but I would really like to know what I don't understand which led me to the wrong answer.