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) $2.5R$
At the top of the loop (height $2R$) it needs at least $v^2 = gR$:
$$mgh = mg(2R) + \frac{1}{2}m(gR) \;\Rightarrow\; h = 2.5R$$
Solution by Sreeraj P, M.Sc Physics