A homogeneous structural steel (ASTM A36) rectangular bar moves on a non-smooth plane, inclined at an angle of 30?with respect to the horizontal (see figure). The block is of length, lx= 8 in, of height, ly =1.5 in, and of width (into the plane of the figure), lz =3 in. The coefficient of (kinetic) friction between the steel bar and the plane is 0.3. The coordinate system to be used is as shown in the figure.

a. Determine the average shear stress (including sign; if positive, no sign is needed) acting on the bar at the inter face of the bar the plane.

b. At what distance along the plane form the lower left corner of the bar does the resultant normal reaction force on the bar act?