Question

A steel wire has an ultimate strength of above $2.0\times {10}^{7}kg-wJ/m^2$ . How large a load can a
0.7$cm$ in diameter steel wire hold before breaking?

• A. $700kg-wt$
• B. $770kg-wt$
• C. $300kg-wt$
• D. None

Answer 1

The correct option is B $770kg-wt$

$\begin{array}{c}\text{Given. -}\\ \text{Strength ef wire}=2\times {10}^{7}kg-wt/m^2=\text{stress.}\\ \text{stress}=\frac{F}{A}\end{array}$

$\begin{array}{cc}F& =\mathrm{stress}xA\\ & =2\times {10}^7\times \frac{\pi }{4}\times {(0.7\times {10}^{-2})}^2\text{.}\text{Kg-wt}\\ & =\frac{49}{2}\times \pi \times 10\\ F& =770kg\text{- wt.}\end{array}$

$\begin{array}{c}\text{max. load. holded with out breaking af wire}\\ =770kg\text{-wt.}\end{array}$