A book is at rest on a table. Table is slowly tipped until book begins to slide. At what angle will book begin to move?

Question

A book is at rest on a horizontal table. The table is steadily and slowly tipped until the book begins to slide off the table.
At what angle, in degrees, will the book begin to move?

Answer 1

depends on the friction generated between books and table.

Answer 2

at atan(mu) where mu is the coefficient of friction between the book and the table and is called angle of repose