The 2-D stress state at a point $P$ in the $x-y$ coordinate system is $\left[\begin{array}{rr}60 & 50 \\ 50 & -40\end{array}\right] M P a$. The magnitude of the tangential stress (in $M P a$ ) on a surface normal to the $x$ -axis at $P$ is___________
The 2-D stress state at a point $P$ in the $x-y$ coordinate system is $\left[\begin{array}{rr}60 & 50 \\ 50 & -40\end{array}\right] M P a$. The magnitude of the tangential stress (in $M P a$ ) on a surface normal to the $x$ -axis at $P$ is___________