Question

What force is required to stretch a steel wire $1c{m}^2$ in cross section to double its length? (Youngs modulus for steel is $2\times {10}^{11}Pa$)

• A. $3\times {10}^{7}N$
• B. $2\times {10}^{7}N$
• C. $3\times {10}^{11}N$
• D. $2\times {10}^{11}N$

Answer 1

The correct option is B $2\times {10}^{7}N$

$Area,a={10}^{-4}{m}^{2}Elongation,\Delta l=2l-l=lForcerequired,F=\frac{Ya\Delta l}{l}=\frac{2\times {10}^{11}\times {10}^{-4}\times l}{l}F=2\times {10}^{7}N$