JEE Main 2020 (2 Sep, Shift 2) Physics Q4: Angular Momentum

Question

Two uniform circular discs are rotating independently in the same direction around their common axis passing through their centres. The moment of inertia and angular velocity of the first disc are 0.1 kg-m

^2

and 10 rad s

^{-1}

respectively while those for the second one are 0.2 kg-m

^2

and 5 rad s

^{-1}

respectively. At some instant they get stuck together and start rotating as a single system about their common axis with some angular speed. The Kinetic energy of the combined system is :

(1) $\frac{2}{3}$ J
(2) $\frac{5}{3}$ J
(3) $\frac{10}{3}$ J
(4) $\frac{20}{3}$ JOfficial answer

Official answer

Option 4

NTA final key (Sep 2020).

Accepted Answer

Option 4: $\frac{20}{3}$ J

Answer

$\frac{2}{3}$ J

Answer

$\frac{5}{3}$ J

Answer

$\frac{10}{3}$ J

Answer

$\frac{20}{3}$ J

JEE Main 2 September 2020, Shift 2, Physics Q4

Same idea in other shifts