Angular Momentum Problem: Rotation Rate [Solved]

[JoeyBob]

Homework Statement:

See attached

Relevant Equations:

L=rotation rate*I

First I found the moment of inertia,

I=1.8(5.5^2+3.9^2+4.9^2)

=125.046

Then I tried to find the rotation rate using the equation L=rotation rate*I

rotation rate=3773/125.046=30.173

But the answer is suppose to be 21.263?

 

[haruspex]

First I found the moment of inertia,

I=1.8(5.5^2+3.9^2+4.9^2)

No. The rotation is about the z (k) axis. What are the distances from that axis?

 

[JoeyBob]

No. The rotation is about the z (k) axis. What are the distances from that axis?

Doesn't k hat represent how far something is from the z axis?

 

[haruspex]

Doesn't k hat represent how far something is from the z axis?

No, it is how far it is along the z axis. And you mean the coefficient of $\hat k$. $\hat k$ is the direction of the z axis.

 

[Delta2]

You have to use pythagorean theorem on the i and j coordinates to find the distance from the z-axis.

 

[JoeyBob]

No, it is how far it is along the z axis. And you mean the coefficient of $\hat k$. $\hat k$ is the direction of the z axis.

You have to use pythagorean theorem on the i and j coordinates to find the distance from the z-axis.

Yes.