A2L Item 178
- Description: Determine the mass that would cause a disk to roll up a curb.
- Goal: Problem solving with rotational dynamics
- Source: UMPERG-ctqpe140
- Keywords: Mechanics, Rotational Dynamics, Torque
The question for students:
A disk
on a horizontal surface sits against a curb. A string wound around the
disk is attached to a mass as shown. If R=5 cm and h=2 cm, the largest
m for which the disk will not move is
- Less than 2M
- 2M
- 3M
- 4M
- 5M
- Greater than 5M
- Cannot be determined.
Commentary for teachers:
Answer
(4) When m = 4M the torques about the contact point between the disk and curb balance. Students find this problem very difficult although rather simple. Many have the most difficulty with the simple geometry needed to find the moment arms.