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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 3 August 2021, Shift 1, Physics Q8

Question 8 of 90 in this shift, Physics question 8 of 30, Section A.

A pulley of mass mm and moment of inertia II about its axis is suspended as shown in the diagram. The spring has spring constant ‘kk' and the string does not slip over the pulley. Find the extension in the spring under equilibrium condition.

The figure, in words

A hatched ceiling line. Two vertical strands hang from it: the left one goes straight down and wraps under a circular pulley (dot at centre); the right one hangs from the ceiling as a spring labelled k, and below the spring a string continues down tangent to the right side of the pulley. A label I is printed at the right side of the pulley.
  1. (1)2kmg\frac{2k}{mg}
  2. (2)kmg\frac{k}{mg}
  3. (3)mgk\frac{mg}{k}
  4. (4)mg2k\frac{mg}{2k}Official answer

Official answer

Option 4

NTA final key.

Chapter
System of Particles and Rotational Motion
Topic
Torque and Equilibrium
Idea tested
Torque of Tension on Pulleys

Same idea in other shifts

Asked 3× in all
  1. 28 Jun 2022, Shift 2 · Q59A uniform disc with mass M=4 kg and radius R=10 cm is mounted on a fixed horizontal axle as shown in figure. A block with mass m=2 kg…MediumNumerical valueHas a figure
  2. 9 Jan 2020, Shift 2 · Q3A uniformly thick wheel with moment of inertia II and radius RR is free to rotate about its centre of mass (see fig). A massless string…MediumSingle correctHas a figure

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.