AP Physics 1: Algebra-Based 3.4 C Describe How the Selection of a System Determines Whether the Energy of That System Changes Questions

Choose a system boundary that makes energy accounting clear, and decide whether work or nonconservative interactions transfer energy across that boundary.

Exam points

choose whether Earth, springs or surfaces belong inside a system boundary for energy accounting
determine whether mechanical energy changes from external work or nonconservative interactions
calculate nongravitational or external work from changes in kinetic and potential energy
calculate energy dissipated by friction or air resistance, including a percentage of initial energy
construct or compare energy bar charts and energy-time graphs for different system choices

[Maximum number: 1]

(7 points, suggested time 13 minutes)

A rod with a sphere attached to the end is connected to a horizontal mounted axle and carefully balanced so that it rests in a position vertically upward from the axle. The center of mass of the rod-sphere system is indicated with a ⊗, as shown in Figure 1. The sphere is lightly tapped, and the rod-sphere system rotates clockwise with negligible friction about the axle due to the gravitational force.

A student takes a video of the rod rotating from the vertically upward position to the vertically downward position. Figure 2 shows five frames (still shots) that the student selected from the video.
Note: these frames are not equally spaced apart in time.

Figure 2

The rod-sphere system has mass M and length L, and the center of mass is located a distance $\frac{3}{4} L$ from the axle, shown in Figure 3.

Briefly explain why the rod and sphere gain kinetic energy, even if Earth is not included in the system.

All question bank results loaded

AP Physics 1: Algebra-Based 3.4 C Describe How the Selection of a System Determines Whether the Energy of That System Changes Questions question 1