Question

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

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

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