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## Homework Statement

The figure below shows a small mass, m, moving at an initial speed, v

_{0}, colliding with a stick with

length, L, and mass, M. Both the mass and the stick lie on top of a table. The collision happens at the

tip of the stick. After the collision the mass continues in the same direction, but now with the speed, v.

For a specific value of the ratio m/M, the stick will collide with the small mass a second time. What is

this value, and how far will the small mass have traveled between collisions? Assume that the

collision is elastic.

## Homework Equations

Initial Angular Momentum: (L/2)mv

_{0}

Angular Momentum After Collision: (1/12)mL

^{2}ω + (L/2)mv

## The Attempt at a Solution

I know that the rod and the particle must be moving at same linear velocities for the second collision to happen. What I don't 100% understand is why the angular momentum for the particle after the collision is still (L/2)mv. Initially, the origin is at the center of the rod, but after the collision both the particle and the rod move to the right. I don't understand why, for the particle, the distance for the angular momentum is just (L/2); doesn't this place the origin at the center of mass of the rod, which is now moving and thus a noninertial frame?

Thanks for the help!