A car of mass 2300 kg collides with a truck of mass 4000 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 m/s, and the truck's velocity just before the collision was m/s.

What is the increase in internal energy of the car and truck (thermal energy and deformation) ?

I got the velocity vector after collision as But I am confused on how to get internal energy.