If a 23 N horizontal force is acting on a box and the box remains at rest, then the force of static friction must be ___________.

Answer 1

In order for this box to stay at rest, it must have an equal and opposite static force that will counteract the force that's being applied to it.

If we are assuming that the box is on flat ground, then there are no more horizontal forces besides the static force and the applied force.

Gravity is a vertical force, therefore it does not need to be considered at this moment.

Using the first principle, the box must have an equal and opposite force to counteract it, the static force F_s must be equal to 23 N.