# What is the rotational inertia of the pole

1. Apr 7, 2010

### mybrohshi5

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

A 2.75 m long pole is balanced vertically on its tip. It starts to fall and its lower end does not slip.

the mass of the pole is 12.93 kg

What is the rotational inertia of the pole about an axis through its lower end and perpendicular to the pole?

2. Relevant equations

I = 1/2mr2

3. The attempt at a solution

I = 1/2(12.93kg)(2.75)2

I = 48.9 kgm2

this was wrong so maybe i thought to use the center of the pole as my R since the mass in distributed throughout the pole

I = 1/2(12.93kg)(2.75/2)2

I = 12.22 kgm2

Does this look right?

thanks for any help

2. Apr 7, 2010

### Staff: Mentor

What does the Parallel Axis Theorem say about how to do this problem?

3. Apr 7, 2010

### nickjer

Does your book have a list of moment of inertias for different shapes? And any of those shapes resemble a pole?

4. Apr 7, 2010

### mybrohshi5

yeah it says

I = 1/3 m L^2

thank you :) that worked perfectly