試題詳解

1. A uniform disk of mass m and radius R (so the moment of inertia ) is rotating about its symmetric axis at an angular velocity ω₀. A ring of the same mass m and radius R originally at rest suddenly drops on the disk. The coeffieient of kinetic friction between the disk and the ring is μ. How long does it take for the ring to reach a final angular velocity ω and rotate together with the disk as shown in the right figure? The gravitational acceleration is g.
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