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AP Physics C: Mechanics 3.3 Potential Energy Questions

Analyse gravitational and elastic potential energy by selecting a system and reference, connecting conservative force with energy gradients, and reading energy diagrams.

Syllabus
Effective Fall 2024
Course
AP Physics C: Mechanics

Exam points

  • choose a system and reference before calculating gravitational or elastic potential energy
  • derive potential energy from a conservative force or force from a potential-energy gradient
  • interpret equilibrium, turning points, allowed regions, kinetic energy, and speed from energy curves
  • determine parameters of gravitational, ideal-spring, or nonlinear-spring energy models

Covered syllabus points

3.3.A—Describe the potential energy of a system

Question 1

[Maximum number: 3]

In Scenario 1, a system composed of two springs, A and B, and a block of mass m is at rest on a horizontal surface. Friction between the block and the surface is negligible. Each spring is attached to a fixed wall and the block, as shown in Figure 1. Spring A has a spring constant k and Spring B has a spring constant 2 k. Each spring is at its relaxed length when the block is at position x=0, as shown.

Figure 1

Figure 1

The block is moved to x=x1x=x_{1} and held at rest, as shown in Figure 2.

Figure 2

Figure 2

An energy bar chart can be used to represent the elastic potential energy UAU_{\mathrm{A}} of Spring A, the elastic potential energy UBU_{\mathrm{B}} of Spring B, and the kinetic energy Kblock K_{\text {block }} of the block. On the energy bar chart in Figure 3, draw shaded bars to represent the energy of the system for when the block is at x=x1x=x_{1}.

- The height of the shaded bars should be proportional to the relative values of UA,UBU_{\mathrm{A}}, U_{\mathrm{B}}, and Kblock K_{\text {block }}.

- Any energy that is equal to zero should be represented by a distinct line on the zero-energy line.

Figure 3

Figure 3

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