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NEET 2016 (Phase 2) · Rotational Kinetic Energy, Work & Power

Rotational Kinetic Energy, Work & Power question from NEET 2016 (Phase 2)

Q50NEET 2016 · PHASE 2Medium

Rotational Kinetic Energy, Work & Power

A solid sphere of mass m and radius R is rotating about its diameter. A solid cylinder of same mass and same radius is also rotating about its geometrical axis with an angular speed twice that of the sphere. The ratio of their kinetic energies of rotation (Esphere / Ecylinder) will be

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Answer: (b)

  1. Sphere: Es=12(25mR2)ω2=mR2ω25E_s = \frac{1}{2}\left(\frac{2}{5}mR^2\right)\omega^2 = \frac{mR^2\omega^2}{5}
  2. Cylinder at 2ω2\omega: Ec=12(12mR2)(4ω2)=mR2ω2E_c = \frac{1}{2}\left(\frac{1}{2}mR^2\right)(4\omega^2) = mR^2\omega^2
  3. EsEc=15\frac{E_s}{E_c} = \frac{1}{5}
  4. So the answer is (b) 1: 5.
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