A stone is tied to an extensible string of length l=1m is kept horizontal. If it is released, find the angular speed of the stone when the string makes an angle θ=30o with the horizontal.
 

Dear Student,
Assuming that the wire is inextensible.

Total energy (pt A) = Total energy (pt B)
PE + KE (at A) =PE + KE (at B).

mgr + 0 = mg (1-cos 60) + $\frac{1}{2}m{v}^2$        (v- velocity at point B).
we get v=$\sqrt{10}$=  3.162 m/s