**Goal:** Problem Solving

**Source:** UMPERG-ctqpe164

A uniform disk with mass M and radius R sits at rest on an incline

30° to the horizontal. String is wound around disk and attached to

top of incline as shown. The string is parallel to incline. The

tension in the string is :

- Mg
- Mg/2
- 2Mg/5
- Mg/4
- None of the above
- Cannot be determined

## Commentary:

## Answer

(4) This problem can be solved a variety of ways. The simplest method is

to balance torques about the contact point. This situation is an

excellent one for discussing the advantages of thinking about preferred

points about which to write the rotational dynamics equation.