
At angular position α as shown in the figure, applying conservation of mechanical energy
mgRsinα=21mv2⇒Rmv2=2mgsinα
In the radial direction,
N−mgsinα=Rmv2⇒N=3mgsinα
Now the ratio of centripetal force and normal reaction is,
A=NRmv2=3mgsinα2mgsinα=32. Therefore, A is constant.