# Angular speed of yo-yo

1. May 16, 2008

### cecico

Hi~
This is the question i got
A yo-yo has radius 8.00cm and mass 0.180kg with small hoop.
The yo-yo is released at rest and after yo-yo
descended 75.0cm calculater the angular speed of the rotating yo-yo
and the speed of its center.
I tried to use K=1/2Mv^2+1/2IW^2 but i got weird number....
I have the answer but I need t know how to solve it...
the speed of its center is 2.71m/s.
I'm seriously fall into the deep~~~~ocean.

2. May 16, 2008

### hage567

Don't forget about gravitational potential energy...

3. May 16, 2008

### Dick

The given answer is right. What did you do wrong? You aren't giving us near enough information to tell. What did you use for I?

4. May 17, 2008

### cecico

I use MR^2 for I.........

5. May 17, 2008

### MaGG

Wouldn't I be

$$I = \frac{m r^2}{2}$$

which is the one for a solid disk? Or are we considering the fact that the yo-yo is made up of two disks?

6. May 17, 2008

### Dick

The clue refers to a hoop, so I think the do want you to use mr^2. You get the correct answer that way. But we still don't know enough to tell where cecico went wrong.