Q 11-05-031NEETEAMCET 2007 (Medical)Easy
A ball of mass $0.6$ kg attached to a light inextensible string rotates in a vertical circle of radius $0.75$ m such that it has a speed of $5\ \text{m s}^{-1}$ when the string is horizontal. The tension in the string when it is horizontal on the other side is ($g = 10\ \text{m s}^{-2}$)
Answer: (C) $20$ N
Concept. With the string horizontal, gravity is perpendicular to it; the two horizontal positions have the same speed.
Step 1. Tension. $T = \dfrac{mv^2}{r} = \dfrac{0.6 \times 25}{0.75} = 20$ N.
Answer. $20$ N (Option C).
Solution by Sreeraj P, M.Sc Physics