Question:
A small heavy block is attached to the lower end of a light rod of length I which can be rotated about its clamped upper end. What minimum horizontal velocity should the block be given so that it moves in a complete vertical circle?
Solution:
Minimum velocity at $A=v$
Minimum velocity at $B=0$
By law of conservation of energy
${ }^{\frac{1}{2}} m v^{2}=m g(2 l)$
$v=2 \sqrt{g l}$