**Goal:** Problem solving with rotational kinematics

**Source:** CT151.2S02-39

Two masses, attached to the ends of a rigid massless rod, are rotating

about pivot P as shown in the picture below. The mass two meters from P

has speed 0.5m/s. What is the acceleration of the mass one meter from

P?

- 0.05 m/s
^{2} - 0.0625 m/s
^{2} - 0.125 m/s
^{2} - 0.250 m/s
^{2} - 0.5 m/s
^{2} - 1 m/s
^{2} - None of the above
- Cannot be determined

## Commentary:

## Answer

(2) Every one of the possible wrong responses indicates a common error

that students make. After the problem has been discussed it is useful to

have students find the acceleration of the mass at 2m and see that the

accelerations are in the same ratio as the velocities. Drawing vector

diagrams showing the Δv for each mass is useful for explaining this

relationship.