Sliding Dumbbell

A dumbbell is constructed by fixing small balls each of mass $6\text{ kg}$ at the ends of a light rod of length $135 \text{ m}$ . The dumbbell stands vertically in the corner formed by a friction-less floor. After the bottom end is slightly pushed to the right the dumbbell starts to slide. Acceleration due to gravity is $10 \text{ m/s}^{2}$ . Find the speed of lower ball (in $\text{m/s}$ ) when the upper ball is leaving the wall.