Consider the situation shown in the figure. Suppose all the surfaces are rough. The direction of friction on B due to A

Step-by-step solution

Let us consider the forces acting on block B in the vertical direction. Since the entire system is in equilibrium, block B is also in equilibrium. This means the net vertical force on block B must be zero. The gravitational force acting on block B is its weight ( m_B g ), which pulls it downwards. To balance this downward force, there must be an equal upward force. The only surface in contact with B that can provide this vertical force is the surface of block A . Thus, the static frictional force exerted by A on B