# Angular speed of yo-yo

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.

Homework Helper
Don't forget about gravitational potential energy...

Homework Helper
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?

cecico
I use MR^2 for I...

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?

Homework Helper
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?

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.