Question

A ball of mass $0.6kg$ attached to a light inextensible string rotates in a vertical circle of radius $0.75m$ such that it has a speed of $5m{s}^{-1}$ when the string is horizontal. Tension in string when it is horizontal on other side is $(g=10m{s}^{-2})$

• A. 30N
• B. 26N
• C. 20N
• D. 6N

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, $\theta =90^{\circ }$
Here, $m=0.6kg,r=0.75m,v=5m/s$
Hence, $T=\frac{m{v}^2}{r}+mg\times 0=\frac{m{v}^2}{r}$
$\therefore T=\frac{0.6\times (5{)}^2}{0.75}=20N$