mechanics.

its given a slight displacement in downward direction..forgot to mention dis...

let suppose the displacement in the downward direction
let mass be m
change in potential energy = gain in kinetic energy
initial P.E = mg2r/\Pi (center of mass is at height 2r/\Pi
and final P.E = - mgl/2
\DeltaP.E = mg 2r/\Pi-(-mg\Pir/2)
so we have mgr(\Pi² +4)/2\Pi = 1/2 mv²
so v² = 2mgr(\Pi² + 4)/2\Pi

m should not be there in the expression...other than this it is right.

oooooooo i just forget. by the way thnx