Chapter 12, Problem 68PP

You’ve been hired by your state’s environmental agency to monitor carbon dioxide levels just above rivers, with the goal of understanding whether river water acts as a source or sink of CO₂. You’ve constructed the apparatus shown in Fig. 12.38, consisting of a boom mounted on a pivot, a vertical support, and a rope with pulley for raising and lowering the boom so its end can extend different distances over the river. In addition, there's a separate rope and pulley for dropping the sampling apparatus so it’s just above the river.

FIGURE 12.38 Passage Problem 64–67

When the boom rope is horizontal, it can’t exert any vertical force. Therefore,

1. a. it’s impossible to hold the boom with the boom rope horizontal.
2. b. the boom rope tension becomes infinite.
3. c. the pivot supplies the necessary vertical force.
4. d. the boom rope exerts no torque.