Q 11-05-042NEETJEE MainMedium
A small block slides without friction down a track that ends in a vertical circular loop of radius $R$. The minimum height above the bottom of the loop from which it must be released to go round the loop is
Answer: (A) $2.5R$
Concept. At the top of the loop $v^2 \ge gR$.
Step 1. Energy. $mgh = mg(2R) + \dfrac12mgR$.
Step 2. Height. $h = 2.5R$.
Answer. $2.5R$ (Option A).
Solution by Sreeraj P, M.Sc Physics