---
title: "A uniform thin rod of mass \\(M\\) and length \\(L\\) is suspended vertically from a frictionless pivot at its top end. A small ball of clay with mass \\(m\\) is traveling horizontally with speed \\(v_0\\) when it strikes the rod at a distance \\(y = \\dfrac{2}{3}L\\) below the pivot. The clay sticks to the rod, and the rod-clay system begins to rotate. Which of the following correctly characterizes the conservation of linear momentum and angular momentum for the rod-clay system during the collision?"
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url: "https://nerd-notes.com/ubq/112618/"
date_modified: "2026-04-29T21:42:42+00:00"
---

# A uniform thin rod of mass \(M\) and length \(L\) is suspended vertically from a frictionless pivot at its top end. A small ball of clay with mass \(m\) is traveling horizontally with speed \(v_0\) when it strikes the rod at a distance \(y = \dfrac{2}{3}L\) below the pivot. The clay sticks to the rod, and the rod-clay system begins to rotate. Which of the following correctly characterizes the conservation of linear momentum and angular momentum for the rod-clay system during the collision?

A uniform thin rod of mass \(M\) and length \(L\) is suspended vertically from a frictionless pivot at its top end. A small ball of clay with mass \(m\) is traveling horizontally with speed \(v_0\) when it strikes the rod at a distance \(y = \dfrac{2}{3}L\) below the pivot. The clay sticks to the rod, and the rod-clay system begins to rotate. Which of the following correctly characterizes the conservation of linear momentum and angular momentum for the rod-clay system during the collision?

![A vertical rod of length L is attached to a pivot at the top. A point mass m is shown moving horizontally toward the rod at a speed v_0. The point of impact is marked at a distance 2/3 L below the pivot.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1777498962-Tf6tJA.jpg)

- **A.** Linear momentum is conserved because the force of the collision is internal to the system, and angular momentum is conserved because the pivot is frictionless.
- **B.** Linear momentum is not conserved because the pivot exerts an external horizontal force on the rod, but angular momentum about the pivot is conserved because this external force exerts no torque about the pivot.
- **C.** Neither linear nor angular momentum is conserved because the collision is perfectly inelastic, and a portion of the system's initial mechanical energy is converted into internal energy.
- **D.** Angular momentum about the pivot is not conserved because the clay ball moves in a straight line before the collision, but linear momentum is conserved because there are no external horizontal forces acting on the clay ball before impact.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/112618/*