Question

A load of $1kg$ weight is attached to one end of a steel wire of cross sectional area $1m{m}^2$ and Young's modulus ${10}^{11}N/m^2$. The Other end is suspended vertically from a hook on a wall, then the load is pulled horizontally and released. When the load passes its lowest position the fractional change in length is $(g=10m/s^2)$

• A. ${10}^{-4}$
• B. ${10}^{-3}$
• C. ${10}^3$
• D. ${10}^4$

Answer 1

The correct option is A ${10}^{-4}$

$\begin{array}{c}\frac{F}{A}=Y\frac{\Delta l}{l}\\ \Rightarrow \frac{\Delta l}{l}=\frac{F}{YA}=\frac{1\times 10}{{10}^{11}\times {10}^{-6}}={10}^{-4}m\\ \end{array}$