Question

A block attached to a spring, pulled by a constant horizontal force, is kept on a smooth surface as shown in the figure. Initially, the spring is in the natural state. Then the maximum positive work that the applied force $F$ can do is: (Given that spring does not break)

• A. $\frac{F^2}{K}$
• B. $\frac{2F^2}{K}$
• C. $\infty$
• D. $\frac{F^2}{2K}$

Answer 1

Answer: (B)

$\frac{2F^2}{K}$

Applying work-energy theorem on the block, we get

$Fl-\frac{1}{2}k{l}^2=0$

$l=\frac{2F}{k}$

or

Work done $=Fl=\frac{2F^2}{k}$