Problem $1\mathrm{.}4$ A tensile test is carried out on a bar of mild steel of diameter $2$ cm $.$ yields under a load of $80$ kN $.$ It reaches a maximum load of $150$ kN breaks finally at a load of $70$ kN $.$

Estimate:

$($i$)$ the tensile stress at the yield point;

$($ii$)$ the ultimate tensile stress;

$($iii$)$ the average stress at the breaking point, if the diameter of t fractured neck is $1$ cm $.$