horizontal force of f1 magnitude 10 n is applied to a box on a floor, but the box does not slide. then, as the magnitude of vertical force f2 is increased from zero, do the following quantities increase, decrease, or stay the same: (a) the magnitude of the frictional force ff on the box; (b) the magnitude of the normal force on the box from the floor; (c) the maximum value ff ,max of the magnitude of the static frictional force on the box? (d) does the box eventually slide?