I’m curious to know the size of the book. Though, pretty much anything can be a projectile in rough air or hard landings. A magazine or small paperback would be better, War and Peace.. not so much.
I’m still surprised they allow iPads. I put mine away for take off and landing. It would suck to get hit by my iPad if it goes flying during turbulence or possibly an aborted take off, or rough landing. (I know turbulence can happen without warning)
Granted, my home airport is typically bumpy to fly in and out of.