Question

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 $5m{s}^{-1}$ when the string is horizontal. Tension in string when it h horizontal on other side is $(g=10m{s}^{-}2)$

• A. 30 N
• B. 26 N
• C. 20 N
• D. 6 N

Answer 1

Answer: (C)

Tension in the string when it makes angle $\theta$ with the vertical, $T=\frac{m{v}^2}{r}+mg\cos \theta$ When the string is horizontal, $\theta ={90}^o$ Here, m = 0.6 kg, r = 0.75 m, v = 5 m/ s Hence, $T=\frac{m{v}^2}{r}+mg\times 0=\frac{m{v}^2}{r}$ $\therefore$ $T=\frac{0.6\times {(5)}^2}{0.75}=20N$