Answer:
When the object is at rest, it stays in a balanced condition and so it does not tend to move from its current position unless an external force tend to act on it. When the external force acts on it, there will be a displacement experienced by the object.
When a book is placed on a table, it does not move it is at rest and balanced position. So If you pick up a book from the floor and place it on the table. The potential energy of the book on the desk corresponds to the work required to move the book from the floor to the desk.
