# Homework Help: Rotational Dynamics

1. Jan 22, 2008

### linnus

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

0.14 meter long, 0.15 kg thin rigid rod has a small 0.22 kg mass stuck on one of its ends and a small 0.080 kg mass stuck on the other end. The rod rotates at 1.7 rad/s through its physical center without friction. What is the magnitude of the angular momentum of the system taking the center of the rod as the origin? Treat the masses on the ends as point masses.

2. Relevant equations

I= summation of mr^2
I=1/12mL^2 (for the rod)
L=IW

3. The attempt at a solution
I=1/12(.45)(.14^2)= .000735
L=.000735 (1.7)=.0012495 kgm/s^2

Last edited: Jan 22, 2008
2. Jan 22, 2008

### mjsd

physical center? is that center of mass or something? or midway of rod?

there is contribution from the small masses to moment of inertia

3. Jan 22, 2008

### linnus

I think it means the midway of the rod.

4. Jan 23, 2008

### mjsd

either way you will need to include the two point masses at the two ends