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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedHardMulti-step

JEE Main 26 February 2021, Shift 1, Physics Q4

Question 4 of 90 in this shift, Physics question 4 of 30, Section A.

Find the gravitational force of attraction between the ring and sphere as shown in the diagram, where the plane of the ring is perpendicular to the line joining the centres. If 8R\sqrt{8}R is the distance between the centres of a ring (of mass ‘m’) and a sphere (mass ‘M’) where both have equal radius ‘R’.

The figure, in words

Drawn: on the left an upright ellipse (the ring seen edge-on, drawn as an ellipse) labelled m at its top, with a centre point X and a downward-pointing double-headed arrow marked R from the top to X; on the right a circle (sphere) labelled M at its top, with centre point Y and an arrow marked R from the top to Y. A horizontal line joins X to Y, marked 8\sqrt{8}R.
  1. (1)827⋅GmMR2\frac{\sqrt{8}}{27}\cdot\frac{\mathrm{GmM}}{\mathrm{R}^{2}}Official answer
  2. (2)89⋅GmMR\frac{\sqrt{8}}{9}\cdot\frac{\mathrm{GmM}}{\mathrm{R}}
  3. (3)138⋅GMmR2\frac{1}{3\sqrt{8}}\cdot\frac{\mathrm{GMm}}{\mathrm{R}^{2}}
  4. (4)223⋅GMmR2\frac{2\sqrt{2}}{3}\cdot\frac{\mathrm{GMm}}{\mathrm{R}^{2}}

Official answer

Option 1

NTA final key.

Topic
No close match in our taxonomy
Idea tested
No close match in our taxonomy

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.