1. The problem statement, all variables and given/known data An automobile of mass 3000 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 6 × 106 N/m, and is observed to compress a distance of 4.23 cm as the car is brought to rest. What was the initial speed of the automobile? Answer in units of m/s. 2. Relevant equations F=-kx Ke=(1/2)mv^2 U=(1/2)kx^2 Kf+Uf=Ki+Ui W=Kf-Ki+Uf-Ui 3. The attempt at a solution I'm really not sure where to start. I tried doing KE=U but I know that's not right.