Question 7
Which of the following pairs of forces is an action–reaction pair?
The right answer is the one marked above.
A book pressing down on a table and the table pushing up on the book. There are two objects here — the book and the table — and each force is applied to the other one.
A force applied to a table and the friction on that table are a pair of balanced forces, not an action–reaction pair: the applied force and the friction act on the same object. That is why they can cancel.
Weight and mass are not a pair of forces at all — mass is not a force. Nor are velocity and retardation.