A particle performs rotational motion with an angular momentum ' $L$ '. if frequency of rotation is doubled…

A particle performs rotational motion with an angular momentum ' $L$ '. if frequency of rotation is doubled and its kinetic energy becomes one fourth, the angular momentum becomes.
  1. $\mathrm{L}$
  2. $\frac{L}{4}$
  3. $\frac{L}{8}$
  4. $\frac{L}{2}$

Solution

Kinetic energy $\mathrm{k}=\frac{1}{2} \mathrm{I} \omega^2$ $\begin{aligned} & \therefore \frac{\mathrm{K}_2}{\mathrm{~K}_1}=\frac{\mathrm{I}_2 \omega_2^2}{\mathrm{I}_1 \omega_1^2} \\ & \therefore \frac{1}{4}=\frac{\mathrm{I}_2}{\mathrm{I}_1} \cdot 4 \\ & \therefore \frac{\mathrm{I}_2}{\mathrm{I}_1}=\frac{1}{16} \\ & \frac{\mathrm{L}_2}{\mathrm{~L}_1}=\frac{\mathrm{I}_2 \omega_2}{\mathrm{I}_1 \omega_1}=\frac{1}{16} \times 2=\frac{1}{8} \\ & \therefore \mathrm{L}_2=\frac{\mathrm{L}_1}{8} \end{aligned}$ *

Asked in: MHT CET 2021 (21 Sep Shift 2)

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