Question

suppose your writing desk is tilted a little a book kept on it starts
sliding down show the direction of frictional force acting on it .Show the direct of friction force acting on it. (please answer this question fast)

Answer 1

Firstly, What is friction?
Ans. Two bodies placed in contact can also exert forces parallel to the surfaces in contact. Such type of forces are called frictional force.
Alright?
Now , if there was no frictional force then the object will fall within fractions of seconds. Some how no one has made the frictionless surface.

Answer 2

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.