At bottom of incline (at P ) the potential energy of ball is converted into kinetic energy i.e.. ‌
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mv2=mgh ⇒‌‌v=√2gh .....(i) To complete the vertical circle, the velocity of ball should be at least √5gR. ⇒‌‌v≥√5gR √2gh≥√5gR [From Eq. (i)] ⇒‌‌h≥‌