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Two bodies, a ring and a solid cylinder of the same material, are rolling down without slipping an inclined plane. The radii of the bodies are the same. The ratio of the velocity of the centre of mass at the bottom of the inclined plane of the ring to that of the cylinder is (√x)/2. Then the value of x is ______.

Asked in JEE Main 20th July 2nd Shift 2021 · Rolling on an incline

Answer: 3

Step-by-step solution

Rolling without slipping from rest through a height h: v²=(2gh)/(1+k) with k=I/(MR²).

Ring: k=1, so vᵣ²=gh.

Solid cylinder: k=1/2, so v_c²=(4gh)/3.

(vᵣ²)/(v_c²)=3/4, so (vᵣ)/(v_c)=(√3)/2.

Comparing with (√x)/2 gives x=3.

"Of the same material" tells you the densities match, so the masses differ — but mass cancels out of v, so it never matters.

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