1. The problem statement, all variables and given/known data Two identical cars approach each other on a straight road. The red car has a velocity of 40MPH to the left and the green car has a velocity of 80MPH to the right. A spring is attached to the front bumper so that a head-on collision will be elastic. If the maximum indentation of each bumper is 5cm, what is the spring constant of the bumpers? 2. Relevant equations KE= 1/2 m v2 EPE = 1/2 k x2 3. The attempt at a solution The kinetic energy must be absorbed by the two springs, so KEred car + KEgreen car = 2 * EPE, correct? Doing this I get a value of 320410m, but this doesn't seem right. Shouldn't I be able to get an answer that is not in terms of the mass? Did I set up the equation wrong and somehow the masses should cancel?