AP Physics C Mechanics 2.2: Forces and Free-Body Diagrams

Represent external forces on an object or system with free-body diagrams, preserving force direction, magnitude, and system boundaries.

[Maximum number: 3]

A uniform disk of radius R and mass $m_{\mathrm{d}}$ is attached to a vertical pole by a horizontal axle that passes through the center of the disk. Friction between the axle and the disk is negligible. A lump of clay of mass $m_{\mathrm{c}}$ is attached to the edge of the disk at Point A. The size of the lump of clay is small compared with the radius of the disk. A horizontal string is connected from the pole to the edge of the disk at Point A. The string makes an angle $\theta$ with the line between Point A and the axle, as shown in Figure 1.

On the following representation of the clay-disk system, draw and label the external forces (not components) exerted on the system. Each force must be represented by a distinct arrow that starts on, and points away from, the point at which the force is exerted on the system.

Figure for Question 2.2 Forces and Free-Body Diagrams question 1 — AP Physics C: Mechanics

For drawing and appropriately labeling separate gravitational forces that are exerted on the 1 point disk and the lump of clay and exerted at the correct locations Scoring Note: Drawing a downward gravitational force exerted on the clay-disk system at the correct location can earn this point.

For drawing and appropriately labeling a leftward force exerted on the system at Point A

1 point

For drawing and appropriately labeling a force directed up and right that is exerted on the

1 point
system at the axle, and no extraneous forces are present

Example Responses

Figure for Answer to Question 2.2 Forces and Free-Body Diagrams question 1 — AP Physics C: Mechanics

Scoring Note: Examples of appropriate labels for the gravitational force include $F_{\mathrm{G}}, F_{g}$ , $F_{\text {grav }}, W, m g, M g$ , "grav force," " F Earth on disk," " F on disk by Earth," $F_{\text {Earth on Disk }}$ , $F_{\mathrm{E}, \text { Disk }}$ , and $F_{\text {Disk, } \mathrm{E}}$ . The labels G or g are not appropriate labels for the gravitational force.

Scoring Note: Examples of appropriate labels for the normal force from the axle include $F_{N}$ , $F_{\text {axle }}, N$ , "normal force," and "axle force."

Scoring Note: Examples of appropriate labels for the tension force include $F_{t}, F_{\mathrm{T}}, T$ , $F_{\text {string }}$ , and "Force from string."

All question bank results loaded

Covered syllabus points

2.2 Forces and Free-Body Diagrams question 1