Q$1($a$)$ Classify the structures as shown in Figure Q$1($a$)$ as unstable, determinate or indeterminate. If it is statically indeterminate, indicate the degree of indeterminacy. $(12$ marks$)$

$($i$)$ Truss

$($ii$)$ Arch

$($iii$)$ Frame

$($iv$)$ Frame

Figure Q$1($a$)$

Q$1($b$)$ Explain the meaning of "ductile" and "brittle" in relation to material properties. Sketch typical stress$-$strain diagrams for ductile and brittle materials. List at least one ductile material and one brittle material.

$(8$ marks$)$