Question

A rod AB is placed inside a hollow spherical shell as shown in figure. A force acts between the rod and the shell to prevent the point B from sliding down and another force at A to prevent it from going up. The number of forces to be shown in FBD of the rod is/are

Answer 1

Note that the direction of both normal reactions is along the radius of the sphere and the direction of forces are along the tangent. From the figure, we can see that the rod has a tendency to slip such that point B comes down along the sphere and point A goes up. Hence, the direction of forces at A and B in both cases acts opposite to the tendency of slipping.