The square root of the ratio of moment of inertia of the cross-section to its cross-sectional area is called

Consider the following statements for a compression member

$${\rm I}.\,\,\,\,$$ The elastic critical stress in compression increases with decrease in slenderness ratio

$${\rm II}.\,\,\,\,$$ The effective length depends on the boundary conditions at its ends

$${\rm III}.\,\,\,\,$$ The elastic critical stress in compression is independent of the slenderness ratio

$${\rm IV}.\,\,\,\,$$ The ratio of the effective length to its radius of gyration is called as slenderness ratio

The TRUE statements are

A 12 mm thick plate is connected to two 8 mm plates, on either side through a 16 mm diameter power driven field rivet as shown in the figure below. Assuming permissible shear stress as 90MPa and permissible bearing stress as 270 MPa in the rivet, the rivet value of the joint is

A vertical rod $$PQ$$ of length $$L$$ is fixed at its top end $$P$$ and has a flange fixed to the bottom end $$Q.A$$ weight $$W$$ is dropped vertically from a height $$h\left( { < L} \right)$$ on to the flange. The axial stress in the rod can be reduced by