Sorry, I am new and my attempt I tried converting mgh(gravitational potential energy) into (mv^2)/2 (Kinetic energy)
b being the height i get mgb=mv^2/2 so i get 2gb=v^2
v^2/r^2 is w^2 so i get 2gb/b^2=w^2 which is sqr(2g/b) as the answer
but somehow the answer in the book i use to study is...