Question

One end of a string of length L and cross-sectional area A is fixed to a support and the other end is fixed to a bob of mass m. The bob is revolved in a horizontal circle of radius r, with an angular velocity $\omega$, such that the string makes an angle $\theta$ with the vertical. The increase $\Delta L$ in length of the string is

• A. $\frac{ML}{AY}$
• B. $\frac{MgL}{AYcos\theta }$
• C. $\frac{MgL}{AYsin\theta }$
• D. $\frac{MgL}{AY}$

Answer 1

The correct option is B $\frac{MgL}{AYcos\theta }$

$\Delta L=\frac{TL}{AY}$
Substituting, $T=mg/cos\theta$
$\Delta L=\frac{mgL}{AYcos\theta }$