# Homework Help: Rotational Kinematics (String attached to disk)

1. Nov 27, 2012

### mattj150

1. The problem statement, all variables and given/known data
Determine the relationship between the angular
acceleration of the flywheel, the downward acceleration of the block, and the radius of
the ring.

Known data:
Mass Ring: 1.420 kg
Radius Ring (Inside, then Outside): 5.10 cm, 6.325 cm
Mass Disk: 1.455 kg
Mass Shaft: Negligable

2. Relevant equations

ω=ω0 + αt
f=ma

3. The attempt at a solution
I'm really lost on this, i assume that i need to calculate the tension the block places on the string (F=MA)? Could anyone give me a hint on how to get started on this.

#### Attached Files:

• ###### image.PNG
File size:
4 KB
Views:
144
2. Nov 27, 2012

### Simon Bridge

Welcome to PF;
hint: draw free-body diagrams.

Though you could use conservation of energy and assume acceleration is constant.

3. Nov 27, 2012

### mattj150

I understand how to do the FBD for the hanging mass. The forces acting on it are simply Fg and Ft. How would i do a FBD for the spinning mass? Would i pick a point on the outer edge to do it for?

4. Nov 27, 2012

### Simon Bridge

The tension force acts at a particular location on the flywheel - creating a torque. $\tau=I\alpha$