Question

Mark's physics book is on the desk. Mark pushes horizontally (from the side) on the book, but the book does not move.

Answer 1

Im pretty sure its diagram b

Answer 2

In order for the book to move, the sum of horizontal forces needs to be "unbalanced" and positive AND in the direction of the push. By "Unbalanced," I mean the forces are not equal. Only two of the diagrams shows horizontal forces and of of these, only one of these is unbalanced. If the forces are balanced, then there is no movement.

Now what do you think?