Trolley A has a mass of 2kg and is moving at 2m/s. It collides with trolley B, which has the same mass but is stationary. What is the momentum of the two trolleys after the collision?

Assuming your two trolleys stick together after the collision, your momentum equation would be M1V1+M2V2 = (M1+M2) V3 and since V2 is 0, then 2x2 = (2+2) V3, thereore the final velocity would be 1, wich would make the final momentum 4