Question

A sphere of radius $25$cm and mass $1$ kg is hung by a string of negligible mass and length $40$ cm, then tension in the string is:-

• A. 12.81 N
• B. 18.4 N
• C. 10 N
• D. 8 N

Answer 1

The correct option is A 12.81 N

Angle made with horizontal

$={\cos }^{-1}\left(\frac{25}{4}\right)=51.317$

From force balance

vertical component of tension $=mg$

$\begin{array}{c}T\sin \theta =mg\\ T\sin 51.37=1\left(10\right)\\ T=\frac{10}{0.78114}=12.8N\end{array}$