A2L Item 081

• Description: Identify the principle that leads to most efficient solution of the problem.
• Goal: Develop a strategic approach to problem solving.
• Source: UMPERG
• Keywords: Problem Solving, Mechanics, Angular Momentum, Reasoning

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The question for students:

A bug walks on a rotating disk. Given: M_bug, I_disk, R_disk, and ω_o when the bug is at r₁. The bug crawls to r₂. Find ω_final 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

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Commentary for teachers:

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.

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