Question

suppose your writing desk is tilted to a position where a book kept on it just start sliding down .the figure showing the correct direction of frictional force acting on it is​

Answer 1

When a book slides on the writing desk, a frictional force acts between the book and the surface of the desk. The direction of frictional force on the book is opposite to the direction of its motion and acts in upward direction, as shown in the figure alongside.