posted by Shelly .
An automobile of mass 2000 kg is driven into a brick wall in a safety test. The bumper behaves like a Hooke’s-law spring. It has an effective spring constant of 5 × 106 N/m, and is observed to compress a distance of 8.7 cm as the car is brought to rest. What was the initial speed of the automobile?
Answer in units of m/s
i used PE=(.5)(k)(d^2)
then from there im not sure what do to, did i do that part and where do i go from there?