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AP Physics C Mechanics 3.4: Selecting the Energy System

Choose a system boundary that makes energy accounting clear and determine whether work transfers energy across that boundary.

Syllabus
Effective Fall 2025
Course
AP Physics C: Mechanics

3.4.C—Describe how the selection of a system determines whether the energy of that system changes 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

In Scenario 1, the block oscillates with period T. The position x of the block in Scenario 1 as a

function of time t is shown in Figure 4.

Scenario 1

Scenario 1

In Scenario 2, the block-springs system is placed on a new surface. There is friction between

the block and the new surface. The block is again moved to the same position x=x1x=x_{1} and

released from rest. The block completes multiple oscillations with the same period as in

Scenario 1 before coming to rest.

On the axes shown in Figure 5, sketch a graph of the kinetic energy K of the block as a

function of t for Scenario 2.

Scenario 2

Scenario 2

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