Conservation of Angular Momentum Video Lessons

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Problem: Disk A, with a mass of 2.0 kg and a radius of 40 cm, rotates clockwise about a frictionless vertical axle at 20 rev/s. Disk B, also 2.0 kg but with a radius of 30 cm, rotates counterclockwise about the same axle, but a greater height than disk A, at 20 rev/s. Disk B slides down the axle until it lands on top of disk A, after which they rotate together.After the collision, what is magnitude of their common angular velocity (in rev/s)?

FREE Expert Solution

In this problem, we're going to use the law of conservation of angular momentum, which is given by:

IAωA+IBωB=(IA+IB)ω, where I is the moment of inertia and ω is the angular velocity. 

The moment of inertia of a disk about the axis is:

I=12MR2

Since disk B is rotating counterclockwise, we'll take its angular omentum to be negative.

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Problem Details

Disk A, with a mass of 2.0 kg and a radius of 40 cm, rotates clockwise about a frictionless vertical axle at 20 rev/s. Disk B, also 2.0 kg but with a radius of 30 cm, rotates counterclockwise about the same axle, but a greater height than disk A, at 20 rev/s. Disk B slides down the axle until it lands on top of disk A, after which they rotate together.

After the collision, what is magnitude of their common angular velocity (in rev/s)?

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