Moment of Inertia and Radius of gyration PYQs: JEE Mains Physics

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1. 1. A circular disc has radius \(R_1\) and thickness \(T_1\). Another circular disc made of the same material has radius \(R_2\) and thickness \(T_2\). If the moment of inertia of both discs are same and \(\frac{R_1}{R_2}=2\) then \(\frac{T_1}{T_2}=\frac{1}{\alpha}\).The value of \(\alpha\) is __________ . 2026 Hard
2. 2. A solid sphere of mass 5 kg and radius 10 cm is kept in contact with another solid sphere of mass 10 kg and radius 20 cm. The moment of inertia of this pair of spheres about the tangent passing through the point of contact is __________ \( kg.m^{2} \). 2026 Easy
3. 3. A solid sphere of mass \(M\) and radius \(R\) is divided into two unequal parts. The smaller part having mass \(M/8\) is converted into a sphere of radius \(r\) and the larger part is converted into a circular disc of thickness \(t\) and radius \(2R\). If \(I_1\) is moment of inertia of a sphere having radius \(r\) about an axis through its centre and \(I_2\) is the moment of inertia of a disc about its diameter, the ratio of their moment of inertia \(I_2/I_1 = \) _____. 2026 Hard
4. 4. A solid sphere of radius 10 cm is rotating about an axis which is at a distance 15 cm from its centre. The radius of gyration about this axis is \(\sqrt{n}\) cm. The value of n is 2026 Easy
5. 5. A solid sphere of radius \(4\) cm and mass \(5\) kg is rotating (rotation axis is passing through the centre of the sphere) with an angular velocity of \(1200\) rpm. It is brought to rest in \(10\) s by applying a constant torque. The torque applied and the number of rotations it made before it comes to rest are _______ and _______ respectively. 2026 Medium
6. 6. A uniform solid cylinder of length \(L\) and radius \(R\) has moment of inertia about its axis equal to \(I_1\). A small co-centric cylinder of length \(L / 2\) and radius \(R / 3\) carved from this cylinder has moment of inertia about its axis equals to \(I_2\). The ratio \(I_1 / I_2\) is _________ . 2026 Hard
7. 7. Moment of inertia about an axis \(AB\) for a rod of mass \(40\) kg and length \(3\) m is same as that of a solid sphere of mass of \(10\) kg and radius \(R\) about an axis parallel to \(AB\) axis with separation of \(3\) m as shown in figure below. The value of \(R\) is given as \(\sqrt{\dfrac{\alpha}{2}}\). The value of \(\alpha\) is _______.
   2026 Medium
8. 8. Suppose there is a uniform circular disc of mass M kg and radius r m shown in figure. The shaded regions are cut out from the disc. The moment of inertia of the remainder about the axis A of the disc is given by \(\frac{ x }{256} Mr ^2\). The value of x is ___________.
   2026 Easy
9. 9. The moment of inertia of a square loop made of four uniform solid cylinders, each having radius R and length \(L ( R < L )\) about an axis passing through the mid points of opposite sides, is (Take the mass of the entire loop as M ) : 2026 Hard
10. 10. Two circular discs of radius each 10 cm are joined at their centres by a rod of length 30 cm and mass 600 gm as shown in figure.
    If the mass of each disc is 600 gm and applied torque between two discs is \(43 \times 10^{5}\) dyne cm, the angular acceleration of the discs about the given axis \(AB\) is ___________\(rad/s^{2}\).
    2026 Hard
11. 11. Two identical thin rods of mass M kg and length L m are connected as shown in figure. Moment of inertia of the combined rod system about an axis passing through point P and perpendicular to the plane of the rods is \(\frac{x}{2} M L^2 kg m ^2\). The value of \(x\) is _________.
    2026 Easy
12. 12. Two masses 400 g and 350 g are suspended from the ends of a light string passing over a heavy pulley of radius 2 cm . When released from rest the heavier mass is observed to fall 81 cm in 9 s . The rotational inertia of the pulley is _________ \(kg \cdot m ^2\).\(\left( g =9.8 m / s ^2\right)\) 2026 Hard
13. 13. \(\mathrm{A}, \mathrm{B}\) and C are disc, solid sphere and spherical shell respectively with same radii and masses. These masses are placed as shown in figure.
    
    The moment of inertia of the given system about \(P Q\) is \(\frac{X}{15} I\), where \(I\) is the moment of inertia of the disc about its diameter. The value of x is _______. 2025 Medium
14. 14. A rod of linear mass density ' \(\lambda\) ' and length ' \(L\) ' is bent to form a ring of radius 'R'. Moment of inertia of ring about any of its diameter is : 2025 Hard
15. 15. A uniform circular disc of radius ' R ' and mass ' M ' is rotating about an axis perpendicular to its plane and passing through its centre. A small circular part of radius \(\mathrm{R} / 2\) is removed from the original disc as shown in the figure. Find the moment of inertia of the remaining part of the original disc about the axis as given above.
    2025 Medium
16. 16. M and R be the mass and radius of a disc. A small disc of radius \(R / 3\) is removed from the bigger disc as shown in figure. The moment of inertia of remaining part of bigger disc about an axis AB passing through the centre O and perpendicular to the plane of disc is \(\frac{4}{x} M R^2\). The value of \(x\) is ________.
    2025 Hard
17. 17. Moment of inertia of a rod of mass ' M ' and length 'L' about an axis passing through its center and normal to its length is ' \(\alpha\) '. Now the rod is cut into two equal parts and these parts are joined symmetrically to form a cross shape. Moment of inertia of cross about an axis passing through its center and normal to plane containing cross is : 2025 Medium
18. 18. The moment of inertia of a circular ring of mass \(M\) and diameter r about a tangential axis lying in the plane of the ring is : 2025 Easy
19. 19. The moment of inertia of a solid disc rotating along its diameter is 2.5 times higher than the moment of inertia of a ring rotating in similar way. The moment of inertia of a solid sphere which has same radius as the disc and rotating in similar way, is \(n\) times higher than the moment of inertia of the given ring. Here, \(\mathrm{n}=\)_________
    Consider all the bodies have equal masses. 2025 Hard
20. 20. Two iron solid discs of negligible thickness have radius \(R_1\) and \(R_2\) and moment of intertia \(I_1\) and \(I_2\), respectively. For \(R_2=2 R_1\), the ratio of \(I_1\) and \(I_2\) would be \(1 / x\), where \(\mathrm{x}=\) ________ - 2025 Easy
21. 21. Four particles each of mass \(1 \mathrm{~kg}\) are placed at four corners of a square of side \(2 \mathrm{~m}\). Moment of inertia of system about an axis perpendicular to its plane and passing through one of its vertex is_________ \(\mathrm{kgm}^2\).
    2024 Hard
22. 22. Ratio of radius of gyration of a hollow sphere to that of a solid cylinder of equal mass, for moment of Inertia about their diameter axis \(A B\) as shown in figure is \(\sqrt{\frac{8}{x}}\). The value of \(x\) is _______.
    2024 Hard
23. 23. Three balls of masses \(2 \mathrm{~kg}, 4 \mathrm{~kg}\) and \(6 \mathrm{~kg}\) respectively are arranged at centre of the edges of an equilateral triangle of side \(2 \mathrm{~m}\). The moment of inertia of the system about an axis through the centroid and perpendicular to the plane of triangle, will be _______\(\mathrm{kg} \mathrm{m}{ }^2\). 2024 Hard
24. 24. Two identical spheres each of mass \(2 \mathrm{~kg}\) and radius \(50 \mathrm{~cm}\) are fixed at the ends of a light rod so that the separation between the centers is \(150 \mathrm{~cm}\). Then, moment of inertia of the system about an axis perpendicular to the rod and passing through its middle point is \(\frac{x}{20} \mathrm{~kg} \mathrm{~m}^2\), where the value of \(\mathrm{x}\) is _______. 2024 Hard
25. 25. A ring and a solid sphere rotating about an axis passing through their centers have same radii of gyration. The axis of rotation is perpendicular to plane of ring. The ratio of radius of ring to that of sphere is \(\sqrt{\frac{2}{x}}\). The value of \(x\) is \(.......\) 2023 Medium
26. 26. A solid sphere and a solid cylinder of same mass and radius are rolling on a horizontal surface without slipping. The ratio of their radius of gyrations respectively \(\left( k _{\text {sph }}: k _{ cyl }\right)\) is \(2: \sqrt{ x }\), then value of \(x\) is ............. 2023 Medium
27. 27. A uniform solid cylinder with radius \(R\) and length L has moment of inertia \(I_1\), about the axis of cylinder. A concentric solid cylinder of radius \(R^{\prime}=\frac{R}{2}\) and length \(L^{\prime}=\frac{L}{2}\) is caned out of the original cylinder. If \(I_2\) is the moment of inertia of the carved out portion ot the cylinder then \(\frac{I_1}{I_2}=..........\) (Both \(I_1\) and \(I_2\) are about the axis of the cylinder) 2023 Medium
28. 28. \(I _{ CM }\) is moment of inertia of a circular disc about an axis \(( CM )\) passing through its center and perpendicular to the plane of disc. \(I _{ AB }\) is it's moment of inertia about an axis \(A B\) perpendicular to plane and parallel to axis \(CM\) at a distance \(\frac{2}{3} R\) from center. Where \(R\) is the radius of the disc. The ratio of \(I _{ AB }\) and \(I _{ CM }\) is \(x: 9\). The value of \(x\) is \(........\)
    2023 Medium
29. 29. If a solid sphere of mass \(5\,kg\) and a disc of mass \(4\,kg\) have the same radius. Then the ratio of moment of inertia of the disc about a tangent in its plane to the moment of inertia of the sphere about its tangent will be \(\frac{x}{7}\). The value of \(x\) is \(.........\) 2023 Medium
30. 30. Moment of inertia of a dise of mass \(M\) and radius ' \(R\) ' about any of its diameter is \(\frac{ MR ^2}{4}\). The moment of inertia of this disc about an axis normal to the disc and passing through a point on its edge will be, \(\frac{ x }{2} MR ^2\). The value of \(x\) is \(..........\). 2023 Medium
31. 31. Solid sphere \(A\) is rotating about an axis \(PQ\). If the radius of the sphere is \(5\,cm\) then its radius of gyration about \(P Q\) will be \(\sqrt{x} \;cm\). The value of \(x\) is \(................\).
    2023 Medium
32. 32. The moment of inertia of semicircular ring about an axis, passing through the center and perpendicular to the plane of ring, is \(\frac{1}{ x } MR ^2\), where \(R\) is the radius and \(M\) is the mass of semicircular ring. The value of \(x\) will be \(...........\) 2023 Easy
33. 33. Two identical solid spheres each of mass \(2\,kg\) and radii \(10\,cm\) are fixed at the ends of a light rod. The separation between the centres of the spheres is \(40\,cm\). The moment of inertia of the system about an axis perpendicular to the rod passing through its middle point is \(........... \times 10^{-3}\,kg - m ^2\) 2023 Medium
34. 34. Four identical discs each of mass ' \(M\) ' and diameter ' \(a\) ' are arranged in a small plane as shown in figure. If the moment of inertia of the system about \(OO ^{\prime}\) is \(\frac{ x }{4} Ma ^{2}\). Then, the value of \(x\) will be \(......\)
    2022 Medium
35. 35. Match List\(-I\) with List\(-II\)

    List \(-I\)	List \(-II\)
    \((A)\) Moment of inertia of solid sphere of radius \((R)\) about any tangent	\((I)\)  \(\frac{5}{3} MR ^{2}\)
    \((B)\) Moment of inertia of hollow sphere of radius \((R)\) about any tangent	\((II)\) \(\frac{7}{5} MR ^{2}\)
    \((C)\) Moment of inertia of circular ring of radius \((R)\) about its diameter.	\((III)\) \(\frac{1}{4} MR ^{2}\)
    \((D)\) Moment of inertia of circular disc of radius \((R)\) about any diameter.	\((IV)\) \(\frac{1}{2} MR ^{2}\)

    Question: Choose the correct answer from the options given below 2022 Medium
36. 36. Moment of Inertia \((M.I.)\) of four bodies having same mass ' \(M\) ' and radius ' \(2 R^{\prime}\) are as follows \(I _{1}=\) \(M.I.\) of solid sphere about its diameter \(I _{2}=\) \(M.I.\) of solid cylinder about its axis \(I _{3}=\) \(M.I.\) of solid circular disc about its diameter \(I _{4}=\) \(M.I.\) of thin circular ring about its diameter If \(2\left(I_{2}+I_{3}\right)+I_{4}=x\). \(I_{1}\) then the value of \(x\) will be....... 2022 Medium
37. 37. The moment of inertia of a uniform thin rod about a perpendicular axis passing through one end is \(I_{1}\). The same rod is bent into a ring and its moment of inertia about a diameter is \(I _{2}\). If \(\frac{ I _{1}}{ I _{2}}\) is \(\frac{ x \pi^{2}}{3}\), then the value of \(x\) will be ............... 2022 Medium
38. 38. The radius of gyration of a cylindrical rod about an axis of rotation perpendicular to its length and passing through the center will be \(....m\) Given, the length of the rod is \(10 \sqrt{3} m\). 2022 Medium
39. 39. A system consists of two identical spheres each of mass \(1.5\, {kg}\) and radius \(50\, {cm}\) at the end of light rod. The distance between the centres of the two spheres is \(5\, {m}\). What will be the moment of inertia of the system about an axis perpendicular to the rod passing through its midpoint ? (in \({kgm}^{2}\)) 2021 Hard
40. 40. A uniform thin bar of mass \(6 \,kg\) and length \(2.4\, meter\) is bent to make an equilateral hexagon. The moment of inertia about an axis passing through the centre of mass and perpendicular to the plane of hexagon is ...... \(\times \,10^{-1} \,kg m ^{2}\) 2021 Hard
41. 41. Consider a badminton racket with length scales as shown in the figure.If the mass of the linear and circular portions of the badminton racket are same \((M)\) and the mass of the threads are negligible, the moment of inertia of the racket about an axis perpendicular to the handle and in the plane of the ring at, \(\frac{r}{2}\) distance from the end \(A\) of the handle will be ....... \(Mr^2\)?
    2021 Hard
42. 42. Consider a uniform wire of mass \(M\) and length \(L\). It is bent into a semicircle. Its moment of inertia about a line perpendicular to the plane of the wire passing through the centre is : 2021 Medium
43. 43. Four identical solid spheres each of mass \('m'\) and radius \('a'\) are placed with their centres on the four corners of a square of side \('b'\). The moment of inertia of the system about one side of square where the axis of rotation is parallel to the plane of the square is 2021 Hard
44. 44. Given below are two statements : one is labelled as Assertion \(A\) and the other is labelled as Reason \(R.\) Assertion \(A :\) Moment of inertia of a circular disc of mass \('M'\) and radius \('R'\) about \(X, Y\) axes (passing through its plane) and \(Z-\)axis which is perpendicular to its plane were found to be \(I_{x}, I_{y}\) and \({I}_{z}\) respectively. The respective radii of gyration about all the three axes will be the same. Reason \(R\) : A rigid body making rotational motion has fixed mass and shape. In the light of the above statements, choose the most appropriate answer from the options given below : 2021 Medium
45. 45. In the given figure, two wheels \(P\) and \(Q\) are connected by a belt \(B\). The radius of \(P\) is three times as that of \(Q\). In case of same rotational kinetic energy, the ratio of rotational inertias \(\left(\frac{{I}_{1}}{{I}_{2}}\right)\) will be \({x}: 1\). The value of \({x}\) will be \(.....\, .\)
    2021 Medium
46. 46. Moment of inertia \((M.I.)\) of four bodies, having same mass and radius, are reported as; \(I _{1}= M\). of thin circular ring about its diameter. \(I _{2}=\) \(M.I.\) of circular disc about an axis perpendicular to the disc and going through the centre, \(I _{3}=\) \(M.I.\) of solid cylinder about its axis and \(I _{4}= M . I.\) of solid sphere about its diameter. Then 2021 Medium
47. 47. Moment of inertia of a square plate of side \(l\) about the axis passing through one of the corner and perpendicular to the plane of square plate is given by 2021 Hard
48. 48. The figure shows two solid discs with radius \({R}\) and \({r}\) respectively. If mass per unit area is same for both, what is the ratio of \({MI}\) of bigger disc around axis \({AB}\) (Which is \(\perp\) to the plane of the disc and passing through its centre) of MI of smaller disc around one of its diameters lying on its plane? Given \('M'\) is the mass of the larger disc. (\(MI\) stands for moment of inertia)
    2021 Medium
49. 49. The solid cylinder of length \(80\, {cm}\) and mass \({M}\) has a radius of \(20\, {cm}\). Calculate the density of the material used if the moment of inertia of the cylinder about an axis \(CD\) parallel to \({AB}\) as shown in figure is \(2.7\, {kg} {m}^{2}\)
    2021 Hard
50. 50. \(ABC\) is a plane lamina of the shape of an equilateral triagnle. \(D,\) \(E\) are mid points of \(AB\), \(AC\) and \(G\) is the centroid of the lamina. Moment of inertia of the lamina about an axis passing through \(G\) and perpendicular to the plane \(ABC\) is \(I _{0} .\) If part \(ADE\) is removed, the moment of inertia of the remaining part about the same axis is \(\frac{ NI _{0}}{16}\) where \(N\) is an integer. Value of \(N\) is
    2020 Hard

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