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Formative assessment questions for teaching physics

A2L Item 173

  • Description: Identify the situation having least angular momentum.
  • Goal: Hone the concept of angular momentum
  • Source: UMPERG-ctqpe132
  • Keywords: Angular Momentum, Mechanics

The question for students:

Which situation has the least (magnitude) angular momentum about the origin?

  1. A 2 kg mass travels along the line y = 3m with speed 1.5 m/s.
  2. A 1 kg mass travels in a circle of r = 4.5 m about the origin with speed 2 m/s.
  3. A disk with I = 3 kg-m2 rotates about its center (on origin) with ω = 3 rad/s.
  1. A
  2. B
  3. C
  4. Both A and B
  5. Both A and C
  6. Both B and C
  7. All have the same magnitude angular momentum

Commentary for teachers:

Answer

(7) Students frequently think that objects traveling in a straight line have no angular momentum. An interesting follow up question is to ask how students would answer if the disk in situation were rotating about the point (1,0).