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 $5\text{ }m{{s}^{-1}}$ 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)

20 N

Answer 2

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, $T=\frac{m{{v}^{2}}}{r}+mg\times 0=\frac{m{{v}^{2}}}{r}$ $\therefore$ $T=\frac{0.6\times {{(5)}^{2}}}{0.75}=20\,N$