The maximum instantancous, produced by an unknown falling weight through a height of $4$ cm

in a vertical bar of length $5$ m and of cross$-$sectional area $5c{m}^2,$ is $1\mathrm{.}80$ mm $.$ Determine : $($i$)$ the

instantaneous stress induced in the vertical bar and $($ii$)$ the values of unknown weight.

Take $E=2{10}^{6}kg\frac{f}{c}{m}^2.$

$[$Ans$.($i$)72\frac{N}{m}{m}^2$ and $($ii$)775\mathrm{.}1$ N $]$