Figure (8-E14) shows a tight rod of length l 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 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?
The length of the height is given as 
Given
The length of the tight rod is given as “l”, the gap between the final and initial position of the ring is given as “h”
Formula Used
The formula for the total energy in terms of kinetic and potential energy is given as
where
The 
is the total energy in terms of kinetic and potential energy, m is the mass of the object, g is the acceleration in terms of gravity and l is the length of the object.
Explanation
The energy is given as total in form of the static and dynamic form of energy which is
The potential energy of the block is given as
Now equating the equations of energy we find the gap of the final and initial position of the ring that is “h”.
The value of the height can only be minimum if and only if the velocity of the object is nullified meaning the value of the velocity is taken as 
, Hence, giving the height between final and initial gap of the ring placement as
Hence, the length of the height is given as
.