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AP Physics C: Mechanics 2.7 A Describe Kinetic Friction Between Two Surfaces Questions

Describe sliding friction by relating kinetic-friction magnitude to the normal force and applying it to horizontal, inclined, circular, stopping, and experimental motion.

Syllabus
Effective Fall 2024
Course
AP Physics C: Mechanics

Exam points

  • apply kinetic friction equals coefficient times normal force with the correct force direction
  • determine how an angled applied force changes the normal force and kinetic friction
  • analyse sliding acceleration and direction changes on a rough inclined plane
  • derive stopping time or distance for motion slowed by kinetic friction
  • use kinetic friction as a tangential or radial force in constrained curved motion

AP Physics C: Mechanics 2.7 A Describe Kinetic Friction Between Two Surfaces Questions question 1

[Maximum number: 2]

A uniform disk and ring, each of mass M and radius R, roll without slipping along a horizontal surface, as shown in Figure 1. The outer edges of the disk and ring are made of the same material. The center of mass of the disk and the center of mass of the ring each initially move with the same constant speed v.

The disk and the ring then smoothly transition to a ramp that is inclined at an angle θ\theta above the horizontal. Both the disk and the ring continue to roll without slipping as they move up the ramp, as shown in Figure 2.

The ring travels a greater distance along the ramp than the disk travels before each momentarily comes to rest.

Figure 1

Figure 1

Figure 2

Figure 2

In a different scenario, the centers of mass of the original disk and ring each have the same initial speed v as they did in the original scenario. The ramp is replaced by a new ramp on which the disk and the ring initially slip as they roll up the new ramp.

Indicate whether the magnitude of the kinetic frictional force exerted on the disk by the new ramp is greater than, less than, or equal to the magnitude of the kinetic frictional force exerted on the ring by the new ramp while both are slipping.

Briefly justify your answer.

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