Question

A 1kg book sits on a horizontal frictionless table in outer space, where there is no gravity. A 9.8N force acts diagonally downwards on the book; there is a 30 degree angle between that force and the vertical.

Draw a force diagram for the book.

Answer 1

Let's analyze the situation from the table's perspective first... it might help sort out the confusion. See, from the table's point of view, all it feels is a strange force pushing it down (because the book is sliding in a friction less fashion so there's no horizontal forces on the table). Ok so that's all the table feels, a force down from something. But this tells you something about the forces that must be acting on the book. (Newton's third law)