Question

a student has six textbooks, each has a thickness of 3.6cm and a weight of 28 N. What is the minimum work the student would have to do to place all of the books in a single vertical stack, starting with all the books on the surface of the table?

Answer 1

Since all of the books are on the table, the 1st book doesn't have to be
lifted:

d =d1 + d2 + d3 + d4 + d5 + d6,
d = 0 + 1*3.6 + 2*3.6 + 3*3.6 + 4*3.6
+ 5*3.6,
d = 0 + 3.6 + 7.2 + 10.8 + 14.4 + 18.

W = F(0 + 3.6 + 7.2 + 10.8 + 14.4 + 18)
W = F * 54cm,
W = 28 * 0.54m = 15.12 Joules.