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## Homework Statement

a disk of radius 40 cm is rotating about an axis through its centre. the moment the inertia of the disk is 0.015 kg m^2 and it is turning at 3 rev/s. sand falls on the disk at a distance of 20 cm from the axis and builds a 20 cm radius sand ring on the disc. How much sand must fall on the disc to slow the speed of revolution to 2 rev/s? Use the law of conversation of angular momentum

## Homework Equations

## The Attempt at a Solution

Angular Momentum L=mvr I know the 40 cm

Moment of Inertia I=mr^2 so mass = .375

How do I approach this problem in what way? what do the rev/s have to do with this problem?