A 2.5 kg block at rest on a tabletop is attached to a horizontal spring having constant 19.6 N/m. The spring is initially unstretched. A constant 20 N horizontal force is applied to the object, causing the spring to stretch. Determine the speed of the block after it has moved 0.900 m from equilibrium if the surface between the block and tabletop is frictionless. I used PE=1/2kx^2 and got 7.938 Then, I used E=1/2mv^2 and plugged 7.938 in for E and solved for v. I found v to be 2.52. I tried the problem another way and got the same answer, I don't understand why it's wrong.