Pasco Collision Carts with built-in velcro ensure that the cart stick together after collision.
Conservation of momentum is applicable, because the force of collision is much higher than the friction. Hence we can assume that there is negligible net external force.
Cart 1 is 1000 g while Cart 2 is 500 g
Author: Leong Tze Kwang, Lim Beng Choo