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MHT CET 2026 (15 Apr, Shift 1) · Rotational Kinetic Energy, Work & Power

Rotational Kinetic Energy, Work & Power question from MHT CET 2026 (15 Apr, Shift 1)

Q8MHT CET 2026 · 15 APR · SHIFT 1Medium

Rotational Kinetic Energy, Work & Power

If the earth suddenly contracts to (13)rd\left(\frac{1}{3}\right)^{\text{rd}} of its present size without change in its mass, the ratio kinetic energy of the earth after and before contraction will be (Earth is assumed to be a rotating sphere about itself)

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Answer: (a)

  1. No external torque, so LL is conserved.
  2. I=25MR2I = \frac{2}{5}MR^2; R′=R3⇒I′=I9R' = \frac{R}{3} \Rightarrow I' = \frac{I}{9}
  3. K=L22I⇒K′K=II′=9K = \frac{L^2}{2I} \Rightarrow \frac{K'}{K} = \frac{I}{I'} = 9
  4. So the answer is (a) 9.
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