A bob is whirled in a horizontal circle by means of a string at an...

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:

Options

A20 rpm
B40 rpm
C5 rpm
D10 rpm

Correct answer

A. 20 rpm

Step-by-step 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}

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