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JEE Main 4 September 2020, Shift 1, Physics Q22

Question 22 of 75 in this shift, Physics question 22 of 25.

A circular disc of mass M and radius R is rotating about its axis with angular speed

\omega_1

. If another stationary disc having radius

\frac{R}{2}

and same mass M is dropped co-axially on to the rotating disc. Gradually both discs attain constant angular speed

\omega_2

. The energy lost in the process is p% of the initial energy. Value of p is __________.

Official answer

20.00

NTA final key (Sep 2020).

Chapter: System of Particles and Rotational Motion
Topic: Angular Momentum
Idea tested: Kinetic Energy Loss in Rotational Coupling

Same idea in other shifts

Asked 5× in all

30 Jan 2024, Shift 1 · Q52Consider a Disc of mass 5 kg, radius 2 m, rotating with angular velocity of 10 rad/s about an axis perpendicular to the plane of rotation.…EasyNumerical valueHas a figure
30 Jan 2024, Shift 2 · Q52Two discs of moment of inertia $I_1 = 4\ kg\,m^2$ and $I_2 = 2\ kg\,m^2$ , about their central axes & normal to their planes, rotating with…EasyNumerical value
27 Aug 2021, Shift 2 · Q3Two discs have moments of intertia $I_1$ and $I_2$ about their respective axes perpendicular to the plane and passing through the centre.…EasySingle correct
2 Sep 2020, Shift 2 · Q4Two uniform circular discs are rotating independently in the same direction around their common axis passing through their centres. The…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.