1. The problem statement, all variables and given/known data The force constant of a spring is 400 N/m and the unstretched length is .65 m. A 2.0 kg block is suspended from the spring. An external force slowly pulls the block down, until the spring has been stretched to a length of .78 m. The external force is then removed, and the block rises. In this situation, when the spring has contracted to a length of .66 m, the acceleration of the block, including direction is closest to: (multiple choices given) 2. Relevant equations I guess since it's a spring problem, the relevant equations would be potential energy=(1/2)kx^2 and maybe F=-kx. 3. The attempt at a solution This problem is from a test I'm correcting so I know that the answer is 7.8 m/s^2 downward. However, I have no idea where to start. I considered that I would use (1/2)(400)(.78-.65)^2-(1/2)(400)(.66-.65)^2 to find the net work done, but I don't know where to go from there. I'm sorry my attempt at a solution is so minimal, but as I said before, I really don't know where to start. If this isn't sufficient enough please tell me.