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## Homework Statement

A horizontal disc of diameter 10 cm is spinning freely about a vertical axis

through its centre at an angular speed of 80 revolutions per minute. A piece

of putty of mass 7.0 g drops on to and sticks to the disc a distance of 3.0 cm

from the centre. The angular speed reduces to 65 revolutions per minute.

Calculate the moment of inertia of the disc.

## Homework Equations

I= MR2

## The Attempt at a Solution

R= 0.03

M= 0.007

but if i use the formula I= MR2,,,, what about the informaton they have given of rev/ min this is the angular speed....

not sure the method to do this???