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JEE Advanced 2024 Paper 2 · Physics · Rotational Motion · medium

A uniform solid sphere of mass m and radius R is projected with speed v0 along a rough horizontal floor with no initial spin. The coefficient of…

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A uniform solid sphere of mass mm and radius RR is projected with speed v0v_0 along a rough horizontal floor with no initial spin. The coefficient of friction between sphere and floor is μ\mu. After it starts rolling without slipping, it moves onto a long, rough incline (the transition is smooth and no energy is lost at the junction; rolling without slipping continues on the incline) and rolls up. The maximum vertical height reached by its centre above its height on the floor is
  1. A. v022g\dfrac{v_0^2}{2g}
  2. B. 25 v0298 g\dfrac{25\,v_0^2}{98\,g}
  3. C. 7 v0210 g\dfrac{7\,v_0^2}{10\,g}
  4. D. 5 v0214 g\dfrac{5\,v_0^2}{14\,g}
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Answer: (D) 5 v0214 g\dfrac{5\,v_0^2}{14\,g}

On the floor, friction acts at the contact point, so angular momentum about any point on the floor line is conserved: mv0R=mvR+25mR2 ωm v_0 R=m v R+\tfrac25 mR^2\,\omega with v=ωRv=\omega R at the end of slipping. This gives v0=75vv_0=\tfrac75 v, so v=57v0v=\tfrac57 v_0 (independent of μ\mu); the rest of the kinetic energy, 27\tfrac27 of the initial value, is lost as heat during slipping. On the incline rolling is without slipping, so mechanical energy is conserved: 12mv2+12⋅25mR2ω2=710mv2=mgh\tfrac12 mv^2+\tfrac12\cdot\tfrac25 mR^2\omega^2=\tfrac{7}{10}mv^2=mgh. Hence h=7v210g=710g⋅25v0249=5v0214gh=\dfrac{7v^2}{10g}=\dfrac{7}{10g}\cdot\dfrac{25v_0^2}{49}=\dfrac{5v_0^2}{14g}. Option (A) assumes no loss of energy during slipping and ignores rotation, (B) ignores the rotational energy on the incline, and (C) assumes no energy loss at all during slipping. The correct option is (D).
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Original question written in the JEE Advanced 2024 Paper 2 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake