$[1]$ The impact force by a falling object acts on a bar that has the same

diameter $)$ and material $($surface stress $Sy=500$MPa, elastic

modulus E$=210$ GPa$).($a$)$ and $($b$)$ have a stress concentration

coefficient $Ki=1\mathrm{.}5$ at the bottom of the bar, and $($b$)$ an additional

notch with $K=3\mathrm{.}2$ and $24$ mm diameter at the middle,

$[1]($a$)$ Find the strain energy density of the bar $[5$ points$]$

$[2]$ Compare the shock energy absorption capacities $($Uno$-$notch$/$U

notch$)$ of $($a$)$ and $($b$).$ However, the volume change of the bar due to the

notch is negligible $[20$ points$]$

$($a$)$ no$-$notch bar

$($b$)$ notch bar