SEE THE SOLUTION WAS GIVEN BY A FRIEND OF MINE TO ME
ets first do it by a simple and short method...
by energy method...
lets work in frame of reference of sphere..
let P be the point where it makes an angle @ with the verticle...
forces acting on particle : pseudo force(=ma); weight(=mg) and normal reaction(=N)
now, K.E at P = Wpseudo force + Wmg + WN
1/2mv2 = maRsin@ + mgR(1-Rcos@) + 0
solve to get v = [2R(asin@ + g -gcos@)]1/2