- #1

bobbles22

- 17

- 0

## Homework Statement

I need a quick sanity check here please. (Sorry, my alphas keep coming out as power signs, they're not!).

To find the force to slow a spinning disc with known moment of inertia (0.0004kgm

^{2}) and known angular velocity (120pi rad/s) to a stop in 6s.

Here, the deceleration ([tex]\alpha[/tex]) is 120pi/6=20 rad/s

^{2}. The radius of the disc is 6cm=0.06m

## Homework Equations

Torque = rf (r=radius, f=force)

Also, torque=I[tex]\alpha[/tex]

And [tex]\alpha[/tex]=w/t where w=angular velocity (120pi) and t= the time to slow=6s.

This gives [tex]\alpha[/tex] to be 20pi rad/s

^{2}.

## The Attempt at a Solution

Setting rf=I[tex]\alpha[/tex]

0.06f=0.0004 x 20pi

From this, the force is given to be 0.42N.

Could someone just check if this is right. I think I've done it ok, but its been some time. It kind of looks right to me, but part of me is thinking I've missed something. It seems too easy. Any help greatly appreciated.