# Rotational Intertia of a disc

1. Nov 28, 2013

### WestCoast

The mass of the disc is M and the radius is R. The problem states:

A disc completes 44 revolutions as it slows from an angular speed of 1.5 rad/sec to a complete stop.

1)W/ acceleration constant, what times is required for it to come to rest?

2) what is the angular acceleration?

3)how much time is required to complete the first half of the 44 revolutions?

This was an in class problem to a intro level class @ college . the teach said we should know how to do this, does anyone know where to get started? I was absent on this day... :)

2. Nov 28, 2013

### bhillyard

Angular Acceleration is constant (given).
So you can use:

V2=us+2fs...........1
With v,u being angular velocity , f angular acceleration, s angular displacement.
Also

v = u + ft..................2

You are given
V = 0, s = 44 x 2 x pi radians, f = ?, U = 1.5 radiant per second

Use equation 2 above to determine f and then equation 1 to find t.

Leave it to you to do part iii.

So far as I can see the mass and radius are a distraction in this as it is constant angular acceleration. It may be that the teacher will lead on to other problems involving the moment of inertia which is calculated from these values.