Question

The box is pushed to the left with 30 N of force, but does not move. What is the Friction Force?​

Answer 1

However here coefficient of friction is not given so unable to calculate.

You can calculate it by below formula.

The formula given by

$\\ \sf\longmapsto F_f=\mu N$

Or

$\\ \sf\longmapsto F_f=\mu mg$

u is coefficient of friction

N is normal reaction.

Here..

box doesn't move means the force if limiting friction is greater than applied force.