Completely inelastic collisions - momentum is conserved but much kinetic energy is lost to other forms of energy, and the objects stick together after collision. Exit Ticket 1 Characterize the following collisions or interactions as completely elastic (100%), partially elastic (less than 100% but objects don't stick together) or completely inelastic: a. two billiard balls rebound off each other in a game of pool b. three protons approach each other and then veer off in opposing directions c. a football player catches a football d. a rocket outside the atmosphere gains altitude, slows down, and returns closer to the planet's atmosphere e. a basketball is bounced 2 A toy train with a mass of 91 g is moving at a speed of 2.3 m/s. It collides with another toy train of mass 121 g. The collision is a completely inelastic collision due to magnets on the train. What will be the final velocity of the trains? Extension . Good Video to watch to understand momentum better. . Video