Question:
Figure (8-E14) shows a light rod of length 1 rigidly attached to a small heavy block at one end and a hook at the other end. The system is released from rest with the rod in a horizontal position. There is a fixed smooth ring at a depth $\mathrm{h}$ below the initial position of the hook and the hook gets into the ring as it reaches there. What should be the minimum value of $h$ so that the block moves in a complete circle about the ring?
Solution:
$v_{\min }=\sqrt{2 g l}$
Total energy at $A=$ Total eneray at $B$
$m g h=\frac{1}{2} m v^{2}[v=\sqrt{2 g l}]$
$h=1$