QUESTION $2$

A thick$-$walled cylinder with an outer and inner diameter of $250$ and $50$ mm $,$ respectively is fabricated from a material with a yield strength of $200$ MPa $.$ An internal pressure of $110$ MPa is expected to cause yielding of the material, thus an external pressure is also required. Determine the magnitude of the external pressure to cause initial yielding of the material.

$(10$ marks$)$