1. The problem statement, all variables and given/known data A car of mass 2200 kg collides with a truck of mass 4500 kg, and just after the collision the car and truck slide along, stuck together, with no rotation. The car's velocity just before the collision was < 35, 0, 0 > m/s, and the truck's velocity just before the collision was < -18, 0, 27 > m/s. 2. Relevant equations Pf=Pi+F*time Ef=Ei+Q+W 3. The attempt at a solution I attempted to use the change in kinetic energy of the system to solve of the change in internal energy. Ef=.5*m*v2 Ef=.5*6700*<-.597,0,18.134>2 <-- final velocity of the system was calculated in an earlier step and found to be correct Ef,sys=<1194,0,1101620> Ei,car=.5*2200*<35,0,0>2 =<1347500,0,0> Ei,truck=.5*4500*<-18,0,27>2 =<72900,0,1640250 EI,sys=Ei,car+Ei,truck = <1420400,0,1640250> I then found the change in energy by Ef,sys-Ei,sys and then getting the magnitude to solve get change in internal energy. This however did not get me the correct answer. I am stuck and not sure what to try.