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Formative assessment questions for teaching physics

A2L Item 176

  • Description: Identify the acceleration of a disk free to move and unwind.
  • Goal: Problem solving with dynamics
  • Source: UMPERG-ctqpe135.3
  • Keywords: Mechanics, Dynamics, Acceleration

The question for students:

Item176_fig1.gif A disk, with radius 0.25 m and mass 4 kg, lies on a smooth horizontal table. A string wound about the disk is pulled with a force of 8N. What is the acceleration of the disk?

  1. 0
  2. 0.5 m/s2
  3. 1 m/s2
  4. 2 m/s2
  5. 4 m/s2
  6. None of the above.
  7. Cannot be determined

Commentary for teachers:

Answer

(4) Students find it difficult to grasp that the angular dynamic relationship does not replace, but rather augments, the 2nd law.