Question 4
A table standing on a level floor is pushed horizontally with a force of 30 N. The table does not move. What is the size of the frictional force acting on the table?
The right answer is the one marked above.
30 N. The table is not moving, so the forces on it balance. Friction has adjusted itself to be equal and opposite to the push.
If friction were more than 30 N the table would slide backwards, towards the person pushing — which plainly does not happen. It matches the push exactly, no more.