A2L Item 081

Goal: Develop a strategic approach to problem solving.

Source: UMPERG

A bug walks on a rotating disk. Given: Mbug,
Idisk, Rdisk, and ωo when the bug
is at r1. The bug crawls to r2. Find
ωfinal for the system.

What principle would you use to solve the problem MOST EFFICIENTLY?

  1. Kinematics only
  2. F = ma or Newton’s laws
  3. Work-Energy theorem
  4. Impulse-Momentum theorem
  5. Angular Impulse-Angular Momentum theorem
  6. Not enough information given

Commentary:

Answer

(5) This problem helps students develop a principle-based approach to
problems. Many students may think correctly that this is a conservation
of angular momentum problem and not recognize that the general principle
is the angular impulse – angular momentum theorem.