Two boxes move at a right angle to each other on a frictionless surface, as shown in the figure below. The mass moving along the taxis has a mass of 6.0 kg and a speed of 1.0 m/s. The mass moving along the y-axis has a mass of 4.0 kg and a speed of 20 my/s. The directions of the two velocity vectors are indicated in the figure. The boxes collide and stick together after the collision. What is their common speed after the collision? . X 6 kg V 2 4 kg