A cart of mass m moving right at speed v collides with an identical cart moving right at half the speed. the carts stick together. what is their speed after the collision

After collison they stick together and have same velocity Vf From the momentum conservation, (m1 + m2) Vf = m1v1 + m2v2 Second is moving with half of first cart speed, (m1 + m2) Vf = m1v + m2v / 2 2 (m1 + m2) Vf = (2m1v + m2v) = >Vf = ((2m1 + m2) v) / 2 (m1 + m2) Identical carts so m1 = m2 = m vf = 3mv / 4m = > Vf = 3v / 4