A2L Item 175

• Description: Identify the acceleration of a mass hanging from a string wound about a disk free to rotate about its center.
• Goal: Problem solving
• Source: UMPERG-ctqpe135.1
• Keywords: Acceleration, Mechanics, Rotational Motion, Tension

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The question for students:

A disk, having radius R and mass M, is free to rotate about an axis through its center. A massless string is wound around disk and attached to mass m. The moment of inertia for a disk given by is 1/2(MR²). If M=4m what is the acceleration of mass m?

1. 0
2. g/2
3. g/8
4. g/5
5. g/3
6. None of the above
7. Cannot be determined

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Commentary for teachers:

Answer

(5) Students answering #2 are likely making the common mistake of thinking that the tension in the string is mg.

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