AP Physics C Mechanics 3.3: Potential Energy

Describe potential energy as a property of system configuration and connect it to conservative interactions and the chosen zero-energy reference.

[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

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

Figure 2

An energy bar chart can be used to represent the elastic potential energy $U_{\mathrm{A}}$ of Spring A,

the elastic potential energy $U_{\mathrm{B}}$ of Spring B, and the kinetic energy $K_{\text {block }}$ 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 $x=x_{1}$ .

- The height of the shaded bars should be proportional to the relative values of $U_{\mathrm{A}}, U_{\mathrm{B}}$ ,

and $K_{\text {block }}$ .

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

Figure 3

A	For indicating that $K_{\text {block }}$ is zero	Point A1
		For drawing bars with positive heights for $U_{\mathrm{A}}$ and $U_{\mathrm{B}}$	Point A2
		For drawing a bar for U_B with a height that is twice the height of the bar drawn for U_A. Scoring Note: This point may be earned regardless of the signs of either bar.	Point A3

Example Response
Figure 3

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3.3.A—Describe the potential energy of a system question 1