(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A light but stiff rod of length R is attached at an angle theta to a shaft along the z-axis; the rod is used to rotate (a single) mass M about the shaft. The mass moves with speed v in a CCW direction. Describe the angular momentum, L, of the mass with respect to the attachment point of the rod.

2. Relevant equations

L = r x p

L = rmv

3. The attempt at a solution

Since L has both horizontal and vertical components, there will be two equations. By the right hand rule, L should be perpendicular to the plane containing the rod (R) and the linear momentum vector (p) and so it points at an angle theta relative to the xy plane in a direction toward the z axis.

The vertical component of L points upward, parallel to the z axis, and so it is positive: Lsin(theta), where L = Rmv.

The horizontal (radial) component is perpendicular to the z axis and pointing inward toward the z axis, so it is positive or negative? I am not sure how to find the sign associated with this horizontal component. I see that it should have a magnitude of Lcos(theta), but I am not sure how to determine the sign.

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# Homework Help: Signs associated with angular momentum

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