Finding Kinetic Energy of a Collision

[Loppyfoot]

Homework Statement

A 900 kg car moving east at 31 m/s runs head-on into a 2800 kg truck moving west at 15 m/s. The vehicles stick together. Use the concept of the center-of-momentum frame to determine how much kinetic energy is lost.

Homework Equations

Kf= Ki(car) + Ki(truck)
K= P^2/(2m)

The Attempt at a Solution

Well I am having difficulty with this problem because I don't know which equations would be suitable for this problem.

Any ideas?

 

[gneill]

How do you think you might go about converting things to the center of momentum frame?