Two blocks that are used in a measuring device have negligible weight. The spring is compressed 6 inches when in the position shown in the diagram below. The end of the screw is very smooth and the coefficient of static friction at all other points of contact is μs = 0.35.

Determine the smallest axial force P which the adjustment screw must exert on B in order to start the movement of B downward.

k = 20 lb/in. A 60 P. B 45