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JEE Main 2005 (AIEEE) · Conservation of Energy

Conservation of Energy question from JEE Main 2005 (AIEEE)

Q38JEE Main 2005 · AIEEEMedium

Conservation of Energy

The upper half of an inclined plane with inclination ϕ\phi is perfectly smooth while the lower half is rough. A body starting from rest at the top will again come to rest at the bottom if the coefficient of friction for the lower half is given by

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Answer: (d)

  1. Let the full length be ll. Body starts and ends at rest, so loss of PE = work against friction on the lower half.
  2. mg lsin⁡ϕ=μmgcos⁡ϕ⋅l2mg\,l\sin\phi = \mu mg\cos\phi \cdot \frac{l}{2}
  3. μ=2sin⁡ϕcos⁡ϕ=2tan⁡ϕ\mu = \frac{2\sin\phi}{\cos\phi} = 2\tan\phi
  4. So the answer is (d) 2tan⁡ϕ2\tan\phi.
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