A2L Item 177

Goal: Problem solving with rotational dynamics

Source: UMPERG-ctqpe135.5

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 angular acceleration of the disk about its

  1. 0
  2. 64 rad/s2
  3. 8 rad/s2
  4. 4 rad/s2
  5. 12 rad/s2
  6. None of the above.
  7. Cannot be determined



(6) The correct value of αcm is 16 rad/s2. Students have the erroneous
concept of ‘conservation of force’. Many think that since the disk
moves, the full force cannot contribute to the torque about the center
of the disk.