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NEET 2025 · Friction on an Incline

Friction on an Incline question from NEET 2025

Q6NEET 2025Medium

Friction on an Incline

There are two inclined surfaces of equal length (L)(L) and same angle of inclination 45∘45^\circ with the horizontal. One of them is rough and the other is perfectly smooth. A given body takes 2 times as much time to slide down on rough surface than on the smooth surface. The coefficient of kinetic friction (μk)(\mu_k) between the object and the rough surface is close to

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Answer: (b)

  1. Same length from rest: L=12at2⇒t∝1aL = \tfrac{1}{2}at^2 \Rightarrow t \propto \dfrac{1}{\sqrt{a}}.
  2. Smooth: a0=gsin⁡45∘a_0 = g\sin 45^\circ; rough: a=gsin⁡45∘(1−μ)a = g\sin 45^\circ(1 - \mu).
  3. trts=2⇒a0a=4⇒1−μ=14\dfrac{t_r}{t_s} = 2 \Rightarrow \dfrac{a_0}{a} = 4 \Rightarrow 1 - \mu = \dfrac{1}{4}
  4. So the answer is (b) μk=0.75\mu_k = 0.75.
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