Q103 / 150 · MHT CET 2026 (16 April Shift 2) · Physics

Solid sphere is rotating about an axis as shown in figure. If the radius of the sphere is 5 cm, then radius of gyration about that axis will be $\sqrt{x}$ cm. The value of x is
Figure

  • A
    $100$
  • Correct answer
    B
    $110$
  • C
    $120$
  • D
    $140$

Solution

The moment of inertia of a solid sphere about an axis passing through its center of mass is given by $I_{cm} = \dfrac{2}{5}MR^2$.

Using the parallel axis theorem, the moment of inertia about the given axis of rotation is:

$I = I_{cm} + Md^2$

where $d$ is the distance from the axis of rotation to the center of mass of the sphere.

Given $R = 5$ cm and $d = 10$ cm, we have:

$I = \dfrac{2}{5}M(5)^2 + M(10)^2$

$I = 10M + 100M = 110M$

The radius of gyration $k$ is defined by $I = Mk^2$.

$Mk^2 = 110M$

$k^2 = 110$

$k = \sqrt{110}$ cm

Comparing this with $\sqrt{x}$ cm, we get $x = 110$.

Hence, the correct answer is option: 'B'.

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