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## Homework Statement

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?

## Homework Equations

KE= 1/2 m v

^{2}

EPE = 1/2 k x

^{2}

## The Attempt at a Solution

The kinetic energy must be absorbed by the two springs, so KE

_{red car}+ KE

_{green 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?