A person's reaction time can be measured by having another person drop a ruler (without warning) through the first person's thumb and forefinger, as shown in Figure 2.17. After observing the unexpected release, the first person grasps the falling ruler as quickly as possible, and the length of the ruler below the top of the finger is noted. Suppose the ruler descends \(18.0 \mathrm{~cm}\) before it is caught. What is the person's reaction time?
THINKING IT THROUGH. Both distance and time are involved. This observation indicates which kinematic equation should be used.