**Goal:** Reason with the concept of moment of inertia

**Source:** UMPERG-ctqpe116

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:

## 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.