Tag Archives: Angular Acceleration

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.

A2L Item 087

Goal: Hone angular kinematic quantities and distinguish them from linear kinematic quantities.

Source: UMPERG

A mass moves in a circle with uniformly increasing anglular velocity.

As the angular velocity ω increases, the linear acceleration of
the mass has…

  1. constant magnitude and direction.
  2. constant magnitude, changing direction.
  3. changing magnitude, constant direction.
  4. both magnitude and direction changing.



(4) This requires exploration. Some students may think that the
direction is changing because the acceleration points toward the center
of the circle. They may be unaware that there is also a component of the
acceleration in the tangential direction.

Some students may answer (3) thinking only of the radial acceleration
and that ‘towards the center’ is a direction.