A2L Item 107
- Description: Determine the unknown mass given ratio of moment of inertia about two axes.
- Goal: Reason with the concept of moment of inertia
- Source: UMPERG-ctqpe116
- Keywords: Angular Velocity, Mechanics, Moment of Inertia
The question for students:
The rotational inertia of the dumbbell (see figure) about axis A is twice the rotational inertia about axis B. The unknown mass is
- 2 kg
- 4 kg
- 5 kg
- 7 kg
- 10 kg
- None of the above
- Cannot be determined
Commentary for teachers:
Answer
(4) Students can get bogged down in calculations when it is unnecessary to do detailed calculations. Proportional distances to the axes is all that is needed. This problem presents a good opportunity to discuss problem solving procedures.