# Use conservation of energy to determine the angular speed of a spool

1. Sep 9, 2010

### mizzy

1. The problem statement, all variables and given/known data

Use conservation of energy to determine the angular speed of a spool after the bucket(3.0kg) has fallen 4.00m, starting from rest.

2. Relevant equations
KE = 1/2mv^2

KEr = 1/2 * I * omega^2

PE - mgh

3. The attempt at a solution

i don't know how to start. I know that i'm suppose to add the change in kinetic translational and kinetic rotational and potential energies.

Can someone guide me on this please?

2. Sep 9, 2010

### rock.freak667

As the bucket falls 4m, what is the energy associated here and what is its quantity?

This energy is converted into translational and rotational kinetic energy, so can you form an equation relating the three equations?

3. Sep 10, 2010

### mizzy

potential energy = -mgh

change in KEt + change in KEr + change in PE

is that right? but what is v in KEt?

4. Sep 10, 2010

### rock.freak667

So you will have mgh=KEt+KEr

you also should know that v=rω.

5. Sep 10, 2010

### mizzy

k. mass of the spool is not given so how can we solve the KEr??

6. Sep 10, 2010

### novop

The m's cancel in the equation.