The cylindrical portion of a thin$-$walled, compressed$-$air tank is made of $5$ mm $-$thick plate welded along a helix at an

angle of $=60$ with the axial direction. The radius of the tank is $250$ mm $.$ If the allowable shearing stress parallel to

the weld is $30$ MPa $,$ calculate the largest internal pressure $p$ that may be applied. $($Ans: $p=2\mathrm{.}77$MPa $)$