Figure 16.18 shows an ultrasonic ruler that is used to

Chapter 16, Problem 16.14

(choose chapter or problem)

Figure 16.18 shows an ultrasonic ruler that is used to measure the distance to a target, such as a wall. To initiate the measurement, the ruler generates a pulse of ultrasonic sound that travels to the wall and, much like an echo, reflects from it. The reflected pulse returns to the ruler, which measures the time it takes for the round-trip. Using a preset value for the speed of sound, the unit determines the distance to the wall and displays it on a digital readout. Suppose that the round-trip travel time is 20.0 ms on a day when the air temperature is 32 C. Assuming that air is an ideal diatomic gas and that the average molecular mass of air is 28.9 u, find the distance between the ultrasonic ruler and the wall.