
Answer:
mg = 30.415 lbf
Explanation:
from figure body of size 3ft*2ft is tend to move down side
weight is divided into two component
vertical component = Â mgcos15 and
horizontal component = mg sin15
considering horizontal component equal to shear force
mgsin15 = \tau A
mgsin15 =\mu \frac{dv}{dh} A
    mg =\frac{ \mu v A}{h*sin15}
       =\frac{8.2*10^{-2}*0.2*3*2}{0.0125*sin15}
    mg = 30.415 lbf