Use conservation of linear momentum.
initial momentum of stopped car (mv = 900kg*0m/s =Â 0)
initial momentum of moving car (mv = 1800kg*34m/s = 61,200 kgs/s)
This must be the momentum afterward.  But the total mass after the cars is entangled is (900+1800 = 2700kg)  This mass times the final velocity, V₂, must equal the total momentum from before the collision. That is:
61,200 = 2700V₂.  Or V₂=61,200/2700 = 22.66m/s  (B)
This is slower than the original velocity so it feels right. Â But be aware that the collision required energy to crush the cars. Â The final velocity of such a collision would be less than this due to the loss in energy of an inelastic collision. Â This is the maximum velocity of the entangled cars, provided no energy was lost in deforming the metal of the cars.
