Let $\mathrm{M}$ and $\mathrm{L}$ be the mass and length of thin uniform rod respectively. In $1^{\text {st…

Let $\mathrm{M}$ and $\mathrm{L}$ be the mass and length of thin uniform rod respectively. In $1^{\text {st }}$ case, axis of rotation is passing through centre and perpendicular to its length. In $2^{\text {nd }}$ case, axis of rotation is passing through one end and perpendicular to its length. The ratio of radius of gyration in first case to second case is
  1. $3: 1$
  2. $1: 2$
  3. $2: 1$
  4. $1: 3$

Solution

$\begin{array}{l}\mathrm{I}_{1}=\frac{\mathrm{ML}^{2}}{12}=\mathrm{MK}_{1}^{2} \\ \mathrm{I}_{2}=\frac{\mathrm{ML}^{2}}{3}=\mathrm{MK}_{2}^{2} \\ \mathrm{k}_{2}=\frac{\mathrm{L}}{\sqrt{3}} \\ \frac{\mathrm{k}_{1}}{\mathrm{k}_{2}}=\frac{1}{2}\end{array} \quad \therefore \mathrm{K}_{1}=\frac{\mathrm{L}}{\sqrt{12}}=\frac{\mathrm{L}}{2 \sqrt{3}}$

Asked in: MHT CET 2020 (14 Oct Shift 1)

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