The radius of gyration of a uniform rod of length l, about

Question:

The radius of gyration of a uniform rod of length $l$, about

an axis passing through a point $\frac{l}{4}$ away from the centre of

the rod, and perpendicular to it, is:

  1. $\frac{1}{4} l$

  2. $\frac{1}{8} l$

  3. $\sqrt{\frac{7}{48}} l$

  4. $\sqrt{\frac{3}{8}} l$


Correct Option: , 3

Solution:

(3) Moment inertia of the rod passing through a point away from the centre of the rod

$I=I g+m \ell^{2}$

$\Rightarrow I=\frac{M I^{2}}{12}+M \times\left(\frac{I^{2}}{16}\right)=\frac{7 M I^{2}}{48}$

Using $I=M K^{2}=\frac{7 M I^{2}}{48} \quad(K=$ radius of gyration $)$

$\Rightarrow K=\sqrt{\frac{7}{48}} I$

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