1. The problem statement, all variables and given/known data We must apply a force of magnitude 80N to hold the block stationary at x = -2.0cm. From that position, we then slowly move the block so that our force does +4.0J of work on the spring-block system; the block is then again stationary. What is the block's position? (Two answers.) 2. Relevant equations F = -kx W = (1/2)*k*xi^2 - (1/2)*k*xf^2 3. The attempt at a solution 80 = -k(-.02m) k = 4000 N/m With the spring constant, i plug it into the Work equation to find xf 4 = .5*4000*(-.02^2) - .5*4000*xf^2 3.2 = -2000xf^2 -.0016 = xf^2 And this is where I am stuck. The answer cannot be an imaginary number, but a real one. I know the equations are correct, so what am I doing wrong? Please explain.