A 1689 kg car collides head on with a 2000 kg truck. The collision is elastic. If the velocity of the truck is 17km/h in the same directions as the car's initial velocity, what is the initial speed of the car in km/h? I'm getting an answer but doesn't seem to make sense. So I'm looking at the conservation of momentum equation to set this up. (1689-kg)(x)+(2000-kg)(0 km/h)=(1689-kg)(0)+(2000-kg)(17 km/h) Then: (1689)(x)=(34000) or x= 20.13 I'm assuming that the final velocity of the car is 0 but it doesn't specifically say in the questions. Can I assume that since it's head on? Also it's a multiple choice question and the closest answer I can find is 19 km/h.