A 2000 kg truck is at rest at a stop sign. A 1100kg car collides head-on with the truck. The car was moving at 15.0m/s before the collision if the collision was completely inelastic, what is the velocity of the car and the truck after the collision?

It's very simple You know linear momentum must be conserved. Initial momentum of truck = 0 Initial momentum of car = 1100x150 kgm/s Collision is inelastic so final velocity will be same for both of them. Final momentum = mass of car+mass of truck) x final velocity. Now according to linear momentum conservation, Pink = Pf solve this to get velocity