Q21

​Q21. A particle of mass m attached to the end of string of length $\mathcal{l}$ is released from the initial position A as shown in the figure. The particle moves in a vertical circular path about O. When it is vertically below O, the string makes contact with nail N placed directly below O at distance h and rotates around it. If the particle just complete the vertical circle about N, then

    $$\begin{gathered} \left(\mathrm{A}\right) \mathrm{h} =\frac{3\mathrm{l}}{5} \left(\mathrm{B}\right) \mathrm{h} =\frac{2\mathrm{l}}{5} \\ \left(\mathrm{C}\right) \mathrm{h} =\frac{\mathrm{l}}{5} \left(\mathrm{D}\right) \mathrm{h} =\frac{4\mathrm{l}}{5} \end{gathered}$$