Q 11-05-041NEETJEE MainTop questionMedium
A body of mass $m$ moves in a vertical circle on a string. The difference between the tensions in the string at the lowest and highest points is
Answer: (D) $6mg$
Concept. Radial equations at bottom and top, linked by energy.
Step 1. Tensions. $T_1 = mg + \dfrac{mv_1^2}{r}$, $T_2 = \dfrac{mv_2^2}{r} - mg$.
Step 2. Energy. $v_1^2 - v_2^2 = 4gr$.
Step 3. Difference. $T_1 - T_2 = 2mg + 4mg = 6mg$.
Answer. $6mg$ (Option D).
Solution by Sreeraj P, M.Sc Physics