A$.$ Multiple Charpy tests should ideally be undertaken at each temperature for improved reliability.

B$.$ The ductile$-$to$-$brittle transition temperature $($DBTT$)$ for the normalised and tempered steel in this graph is somewhere between $-50C$ and $+30C.$

C$.$ This steel grade loses much of its toughness at temperatures below the DBTT$.$

D$.$ The DBTT of steel usually changes with composition.

E$.$ This steel grade has greater ductility at temperatures below the DBTT$.$

$23.$ A wire $2\mathrm{.}5m$ long has a cross$-$sectional area of $2\mathrm{.}5m{m}^2.$ It is hung vertically, and a $4\mathrm{.}5kg$ mass is hung from it$.$ By how much does the wire stretch elastically if Young's modulus for the material is $2\mathrm{.}0{10}^{11}Pa?($acceleration due to gravity $=9\mathrm{.}8m{s}^{-2})$

A$.0\mathrm{.}72mm$

B$.2\mathrm{.}21mm$

C$.0\mathrm{.}0221mm$

D$.0\mathrm{.}221mm$

E$.0\mathrm{.}072mm$

$24.$ What stress applied to a copper wire would produce the same elastic elongation as a $50C$ rise in temperature? $[$Data for $Cu$ : thermal expansivity $=16\mathrm{.}6{10}^{-6}{C}^{-1}$; elastic modulus $=124\mathrm{.}1$GPa $]$

A$.103$MPa

B$.166$MPa

C$.830$MPa

D$.6205$MPa,

E$.11222$MPa