$($a$)$ A rectangular hollow bar with outer dimensions $50$ mm wide $35mm$ high, thickness $10$ mm and length $2\mathrm{.}5$ m is subjected to a $200$ kN axial tensile load. If we know the bar is still elastic and it extends by $2$ mm under this load, find:

$($i$)$ The stress in the bar

$(2$ marks$)$

$($ii$)$ The strain in the bar

$(2$ marks$)$

$($iii$)$ The stiffness of the bar

$(2$ marks

$($b$)$ In Figure Q$4($b$),$ a glass window $($which is an equilateral triangle of side $2$ m $)$ is set within the walls of a fish tank and is held by bolts at its three corners A$,$ B and C$.$ Side A$-$B is parallel with the water surface.

When the container is filled to its maximum capacity, what is the force in each of the three bolts?

$(9$ marks