A uniform chain of mass 6 kg and length 3 m lies on a table with one-third of its length hanging over the edge. The work needed to pull the hanging part back onto the table is (g = 10 m/s²):

As a pendulum swings, total mechanical energy (KE+PE) stays constant: at the highest points A and C, all energy is potential (zero speed); at the lowest point B, all of that energy has converted into kinetic energy (maximum speed).