Question

A spring 40 mm long is stretched by the application of a force. If 10 N force is required to stretch the spring through 1 mm, then work done in stretching the spring through 40 mm is:

• A. 8 J
• B. 23 J
• C. 68 J
• D. 84 J

Answer 1

Answer: (A)

8 J

Answer 2

From the relation $F=kx$ or $k=\frac{F}{x}=\frac{10}{1\times {{10}^{-3}}}={{10}^{4}}N\text{/}m$ and also $F=kx={{10}^{4}}\times 40\times {{10}^{-3}}=400\,N$ Now work done, $W=\frac{1}{2}Fx=\frac{1}{2}\times 400\times 40\times {{10}^{-3}}=8\,J$