A steel bar of solid circular cross-section is 50 mm in diameter. The bar is pinned at both ends and subjected to axial compression. If the limit of proportionality of the material is 210 MPa and E = 200 GPa, determine the m minimum length to which Euler' formula is valid. Also determine the value minimum length.

 A steel bar of solid circular cross-section is 50 mm in diameter. The bar is pinned at both  ends and subjected to axial compression. If the limit of proportionality of the material is  210 MPa and E = 200 GPa, determine the m minimum length to which Euler'  formula is valid. Also determine the value  minimum length.