S storeys Height of each storey=h Figure 2: A building of S identical stories, each of height h. b A building has S stories each of height h as shown in Fig.(2). An ex- plosion destroys the strength of the nth story. You may assume that the building remains intact above the story that explodes and that momentum is conserved in the collisions of the successive stories during the fall of the building. Estimate the time before the (n + 1)th floor hits the ground falling vertically.