The pile driver shown in Fig. 1a has a mass of 100 kg and falls 3 m onto the pile which has a mass of 200 kg. The two become joined on impact. The pile is driven into the ground a distance of 0.08 m each time. The mass is raised by a winch between each impact. The graph in Fig, 1b shows how the velocity of the driver varies with time as it is raised by the winch.