A bob is whirled in a horizontal circle by means of a string at an initial speed of 10 rpm. If the tension…
A bob is whirled in a horizontal circle by means of a string at an initial speed of 10 rpm. If the tension in the string is quadrupled while keeping the radius constant, the new speed is:
20 rpm
40 rpm
5 rpm
10 rpm
Solution
In horizontal circular motion,
$T=m \omega^2 r$
For constant $m$ and $r, T \propto \omega^2$
$T=4 T$ (Given)
$\Rightarrow \omega^{\prime}=2 \omega$
$=20 \mathrm{rpm}$