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Rotational Motion question

2025 · 24 Jan · Shift 2 · Q66
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  5. /2025 · 24 Jan · Shift 2 · Q66

Rotational Motion question

2025 · 24 Jan · Shift 2 · Q66

JEE MainPhysicsRotational MotionMCQ+4 / −1
A solid sphere is rolling without slipping on a horizontal plane. The ratio of the linear kinetic energy of the centre of mass of the sphere and rotational kinetic energy is :
  1. A
    34\frac{3}{4}43​
  2. B
    43\frac{4}{3}34​
  3. C
    52\frac{5}{2}25​
  4. D
    25\frac{2}{5}52​
View written solutionFree

Correct answer: C

  1. Write the expressions for kinetic energies

For a body rolling without slipping:

  • Linear speed of centre of mass = vvv
  • Angular speed = ω\omegaω
  • Condition of rolling: v=Rωv = R\omegav=Rω

The linear kinetic energy of the centre of mass is Klinear=12mv2K_{\text{linear}} = \frac{1}{2}mv^2Klinear​=21​mv2

The rotational kinetic energy about the centre of mass is Krot=12Iω2K_{\text{rot}} = \frac{1}{2}I\omega^2Krot​=21​Iω2


  1. Moment of inertia of a solid sphere about its centre

For a solid sphere, I=25mR2I = \frac{2}{5}mR^2I=52​mR2

So, Krot=12(25mR2)ω2K_{\text{rot}} = \frac{1}{2}\left(\frac{2}{5}mR^2\right)\omega^2Krot​=21​(52​mR2)ω2

Using ω=vR\omega = \frac{v}{R}ω=Rv​, Krot=12⋅25mR2⋅v2R2=15mv2K_{\text{rot}} = \frac{1}{2}\cdot \frac{2}{5}mR^2 \cdot \frac{v^2}{R^2} = \frac{1}{5}mv^2Krot​=21​⋅52​mR2⋅R2v2​=51​mv2


  1. Find the required ratio

KlinearKrot=12mv215mv2=1/21/5=52\frac{K_{\text{linear}}}{K_{\text{rot}}} = \frac{\frac{1}{2}mv^2}{\frac{1}{5}mv^2} = \frac{1/2}{1/5} = \frac{5}{2}Krot​Klinear​​=51​mv221​mv2​=1/51/2​=25​


  1. Check options
  • A: 34\frac{3}{4}43​ ❌
  • B: 43\frac{4}{3}34​ ❌
  • C: 52\frac{5}{2}25​ ✅
  • D: 25\frac{2}{5}52​ ❌

Therefore, the correct answer is: 52\boxed{\frac{5}{2}}25​​ which is Option C.

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