a building is rapidly and inexpensively dismantled by dropping a heavy inverted u - shaped tool on a building or other structure from an elevation thereabove as from the upper outer end of a boom on a crane , the tool is initially suspended from a cable leading back to a winch capable of dropping the tool in a free fall . a secondary cable is attached to one of the arms of the inverted u - shaped tool inwardly from its lower end , the secondary cable leading to a secondary winch of a type capable of exerting great pulling power on the tool once it is engaged in the building or structure being dismantled .