Suppose marble A and B undergo one-dimensional collision. From the conservation of momentum and kinetic energy, the equation of elastic collision can be written. If marble B is initially at rest, then the equations get simplified. On solving the two equations, the final velocity of the marbles A and B can be obtained. If marbles of equal masses collide, then marble A comes to rest after the collision and B travels with the initial velocity of marble A. By solving the equations, it is seen that marbles exchange momentum. If marble B is heavier than marble A, then, after collision, marble A bounces back with almost the same velocity, and marble B moves with a very low velocity. If marble A is heavier than marble B, then marble A continues to move with the same velocity. Marble B gets a push and travels with a higher velocity than the initial velocity of marble A. In the case of marbles of different masses undergoing one-dimensional elastic collisions, the relative velocities before and after the collision have the same magnitude but opposite direction.