Six identical books, 4.0 cm thick and each with a mass of 0.8kg, lie individually on a flat table.How much work would be needed to stack the books one top of the other?

Answer 1

original cg is 2 cm (half of 4) above the table. It will end up at 12 cm.
the center of gravity must be moved up 12 cm- 2 cm = 10 cm = .1 meter

m g h = 6 *.8 * 9.81 * .1 Joules