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

Options

A. (a) `F^2/k`
B. (b) `(2F^2)/(k)`
C. (c) `oo`
D. (d) `(F^2)/(2k)`

Answer

B

Explanation

Applying work-energy theorem on the block, we get
`Fl-1/2kt^2=0`
`l=(2F)/(k)` or work done `=Fl=(2F^2)/(k)`