Figure shows a light 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?

Explanation

The minimum velocity required to cross the height point `c=sqrt2 gl`
Let the rod relesed from a height h.
Total energy at A=total energy at B
`mgh=1/2mv^2`
`mgh=1/2m(2gl)`
[Because v is the required velocity at B such that the block make a complete circle.
Refer Q=49]
So h=l`