**Goal:** Problem solve with rotational dynamics

**Source:** UMPERG-ctqpe156

A

uniform rod is hinged to a wall and held at a 30° angle by a thin

string that is attached to the ceiling and makes a 90° angle to rod.

The tension in the string is 10N. The weight of the rod is about

- 13N
- 18N
- 20N
- 23N
- 40N
- none of the above

## Commentary:

## Answer

(4) Some students will use the wrong trigometric function and

conclude that the weight is 40N.

An interesting follow up question is to ask what is the hinge force.

Students often forget that both the sum of the forces and the sum of the

torques must be zero for static equilibrium.