1. The problem statement, all variables and given/known data Six identical books, 4.0 cm thick and each with a mass of .80 Kg, lie individually on a flat table. How much work would be needed to stack the books one on top of the other. 2. Relevant equations U= mgy 3. The attempt at a solution total mass = .8kg x 6 = 4.8 G= 9.8 y= .004 * 6 = .024 (4.8)(9.8)(.024) = 1.12 J the answer is 4.7 J. What am I doing wrong?