$2-11$ The $125-lb$ girl shown in the figure below is doing a chin$-$up$.$ For the position shown, the humerus is modeled as an axially loaded member. Determine the normal stress at section a$-$a if the section is modeled as

$($a$)($b$)$

a$)$ assume the diameter of the bone is $1$ inch.

b$)$ assume the bone is hollow with an outer diameter of $1$ inch and an inner diameter of $0\mathrm{.}6$ inches.