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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctEasyCalculation

JEE Main 5 September 2020, Shift 1, Physics Q4

Question 4 of 75 in this shift, Physics question 4 of 25.

A wheel is rotating freely with an angular speed ω\omega on a shaft. The moment of inertia of the wheel is I and the moment of inertia of the shaft is negligible. Another wheel of moment of inertia 3I initially at rest is suddenly coupled to the same shaft. The resultant fractional loss in the kinetic energy of the system is :
  1. (1)14\frac{1}{4}
  2. (2)34\frac{3}{4}Official answer
  3. (3)56\frac{5}{6}
  4. (4)0

Official answer

Option 2

NTA final key (Sep 2020).

Chapter
System of Particles and Rotational Motion
Topic
Angular Momentum
Idea tested
Conservation of Angular Momentum

Same idea in other shifts

Asked 7× in all
  1. 6 Apr 2024, Shift 1 · Q56If the radius of earth is reduced to three-fourth of its present value without change in its mass then value of duration of the day of…MediumNumerical value
  2. 8 Apr 2024, Shift 2 · Q35A thin circular disc of mass M and radius R is rotating in a horizontal plane about an axis passing through its centre and perpendicular…EasySingle correct
  3. 10 Apr 2023, Shift 1 · Q53If the earth suddenly shrinks to 164\frac{1}{64}th of its original volume with its mass remaining the same, the period of rotation of earth…MediumNumerical value
  4. 11 Apr 2023, Shift 2 · Q53A circular plate is rotating in horizontal plane, about an axis passing through its center and perpendicular to the plate, with an angular…MediumNumerical value
  5. 26 Jun 2022, Shift 1 · Q35A thin circular ring of mass M and radius R is rotating with a constant angular velocity 2 rads−1\mathrm{rads^{-1}} in a horizontal plane…EasySingle correct
  6. 18 Mar 2021, Shift 1 · Q20A thin circular ring of mass M and radius r is rotating about its axis with an angular speed ω\omega. Two particles having mass m each…EasySingle correct

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. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.