Two identical discs are positioned on a vertical axis as shown in the figure. The bottom disc is rotating at angular velocity ω and has rotational kinetic energy K . The top disc is initially at rest.

Question

Two identical discs are positioned on a vertical axis as shown in the figure. The bottom disc is rotating at angular velocity ω and has rotational kinetic energy K . The top disc is initially at rest. It then falls and sticks to the bottom disc. The change in the rotational kinetic energy of the system is

TestHub · Accepted Answer

2 I ω = I ω 0 ​ ⇒ ω = 2 ω 0 ​ ​ k f ​ = 2 1 ​ ( 2 I ) ω 2 = 2 1 ​ × 2 I × 4 ω 0 2 ​ ​ = 2 1 ​ ( 2 1 ​ I ω 0 2 ​ ) k = 2 k 0 ​ ​ ∴ Δ k = k f ​ − k i ​ = 2 k 0 ​ ​ − k 0 ​ = − 2 k 0 ​ ​

Physics - Rotation Question with Solution | TestHub

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