the force applied needed to move the box is F= 55*9.8*.3 = 161.7 N which is also the max friction force the surface can provide. But the force applied in the problem is 140 N. This is not sufficient to move the box. And the friction will apply a force of 140 N to maintain the box at rest.
Friction force adjusts itself according to the applied force until its limit is reached which in this case is 161.7 N. If a force greater than 161.7 N is applied the box, it would start moving and the friction then acting would be 161.7 N since it can go no higher.
May 14th, 2015
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