Question

A spring $40mm$ long is stretched by applying a force. If $10N$ force is required to stretch the spring through one mm, then work done in stretching the spring through $40mm$ is

• A. $24J$
  
• B. $8J$
  
• C. $56J$
  
• D. $54J$
  

Answer 1

The correct option is B $8J$

$F=k\times x$

$\Rightarrow 10=k\times 0.001$

$\Rightarrow k=10000N/m$

$\Rightarrow Energy=\frac{1}{2}k{x}^2$

$\Rightarrow Energy=\frac{1}{2}\times 10000\times (0.04{)}^2$

$\Rightarrow Energy=8J$

Hence correct answer is option $B$