You are Here: Home >< Maths

# Angular momentum watch

1. The formula for angular momentum about some axis is where is the moment of inertia about the same axis, and is the angular speed.

So here it's just finding , which is fine, I just placed a circle on the xy-plane at the origin and determined over the region .

So the angular momentum is just but the one-liner answer reference says instead.

Is this a typo on the lecturer's part, or is there a point where I was supposed to multiply by 2?
2. (Original post by RDKGames)

Is this a typo on the lecturer's part, or is there a point where I was supposed to multiply by 2?
It's not a typo - you've considered a disc, rather than a circle/hoop.

Edit: Misread the question myself initially.
3. (Original post by ghostwalker)
It's not a typo - you've considered a disc, rather than a circle/hoop.

Edit: Misread the question myself initially.
Ah goodness, thanks

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 22, 2018
Today on TSR

### Top unis in Clearing

Tons of places at all these high-ranking unis

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams