Question

A load of 1kg weight is attached to one end of a steel wire of cross sectional area 3mm${}^2$ and Youngs 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 through its lowest position the fractional change in length is: (g$=$10m/ s${}^2$ )

• A. $0.3\times {10}^{-4}$
• B. $0.3\times {10}^{-3}$
• C. ${10}^3$
• D. ${10}^4$

Answer 1

The correct option is A $0.3\times {10}^{-4}$

$Y=\frac{F/A}{△l/l}$
$\frac{△l}{l}=\frac{F}{YA}$
$=\frac{1\times 10}{{10}^{11}\times 3\times {10}^{-6}}$

$=0.3\times {10}^{-4}$