A 1200-kg car traveling initially with a speed of 25m/s in an easterly direction crashes into the rear end of a 9000-kg truck moving in the same direction at 20m/s. The velocity of the car right after the collision is 18m/s to the east. (a) what is the velocity of the truck right after the collision? (b) how much mechanical energy is lost in the collision? account for this loss in energy.