Circular MotionMedium
Question
A bob is whirled in a horizontal plane by means of a string with an initial speed of $\omega rpm$. The tension in the string is $T$. If speed becomes $2\omega$ while keeping the same radius, the tension in the string becomes:
Options
A.$\frac{T}{4}$
B.$\sqrt{2}T$
C.$T$
D.$4T$
Solution
Sol. [Key Concept: Circular motion — tension when angular speed changes]
$$T = m\mathcal{l}\omega^{2}$$
$$\begin{matrix} & T^{'} = m\mathcal{l}(2\omega)^{2} \\ & T^{'} = 4T \end{matrix}$$
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