A body attached to a string of length $l$ describes a vertical circle such that it is just able to cross the highest point. Find the minimum velocity at the bottom of the circle.

In the figure shown a lift goes downwards with constant retardation. An observer in the lift observers a conical pendulum in the lift, revolving in a horizontal circle with time period $2$ seconds. The distance between the centre of the circle and the point of suspension is $2.0 \mathrm{m}$. Find the retardation of the lift in $\mathrm{m} {\mathrm{s}}^{-2}$. Use ${\mathrm{\pi }}^2 = 10$ and $g=10 \mathrm{m} {\mathrm{s}}^{-2}$