Can the two blocks be in equilibrium in the position shown? Justify your answer. All surfaces are frictionless except the horizontal surface beneath block B.

Given Data:

• The weight of block A is W_A = 120 lb.
• The weight of block B is W_B = 80 lb.
• The coefficient of static friction is ${\mu }_s=0.2.$

The free-body diagram of block A can be drawn as,

Assuming block A to be in the equilibrium, apply force balance in the vertical direction,

$\begin{array}{rcl}N\cos 20°& =& 120 \mathrm{lb}.\\ N & =& 127.7 \mathrm{lb}.\end{array}$

The free-body diagram of the Block B can be drawn as,

Applying force balance in the vertical direction,

$\begin{array}{rcl}R\text{'}& =& N\cos 20°+W_B\\ & =& 120 \mathrm{lb}+80 \mathrm{lb}\\ & =& 200 \mathrm{lb}\end{array}$