$($a$)$

$($b$)$

FIG. P$5.65\mathrm{.}6$ A beam with the square cross section shown carries a maximum bending

moment of $8000$ lb ft$.$ Determine the maximum bending stress if the beam is first

oriented as shown in $($a$),$ and then as shown in $($b$).$ For both orientations, the z$-$axis

is the neutral axis; that is$,$ the axis about which the bending moment acts.