Rod has length l and mass m. Rod stands in vertical position. In one moment rod's end which is on top starts moving down around axis which is placed in rod's second end. Rod is inside gravity field. Note that rod has mass m. It means that rod is rigid body so we can't treat it like material point. Rod's center of gravity is marked in its half of length. Subject of example is to find final velocity of rod's end when it will be on the ground.