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JEE Main 2019 (9 Apr, Shift 1) · Rolling Motion

Rolling Motion question from JEE Main 2019 (9 Apr, Shift 1)

Q68JEE Main 2019 · 9 APR · SHIFT 1Medium

Rolling Motion

The following bodies are made to roll up (without slipping) the same inclined plane from a horizontal plane.: (i) a ring of radius R, (ii) a solid cylinder of radius R/2 and (iii) a solid sphere of radius R/4. If in each case, the speed of the centre of mass at the bottom of the incline is same, the ratio of the maximum heights they climb is:

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Answer: (a)

  1. h=v22g(1+k)h = \dfrac{v^2}{2g}(1+k), independent of radius, so h∝(1+k)h \propto (1+k).
  2. Ring k=1k=1: 22; solid cylinder k=12k=\frac{1}{2}: 32\frac{3}{2}; solid sphere k=25k=\frac{2}{5}: 75\frac{7}{5}.
  3. Ratio 2:32:75=20:15:142 : \frac{3}{2} : \frac{7}{5} = 20 : 15 : 14 (multiply by 10).
  4. So the answer is (a) 20 : 15 : 14.
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