The physics of an ultrasonic ruler. 1. An ultrasonic ruler can be used to measure the distance between itself and a target, such as a wall. To initiate the measurement, the ruler generates a pulse of ultrasonic sound that travels to the wall and, like an echo, reflects from it. The reflected pulse returns to the ruler, which measures the time it takes for the round- trip. Suppose the round-trip travel is 20.0 x 10'3 s on a day when the temperature of the air is 23 OC. . a. Determine the speed of sound in the air at this temperature. . b. Determine the distance to the wall. The physics of wavelength and frequency for a moving radio. 2. A music fan at a swimming pool is listening to a radio on a diving platform. The radio is playing at a constant frequency tone when this person, clutching the portable radio, jumps. Describe the observed frequency or pitch for the following three observers. . a. The person holding the radio. . b. A person left behind on a platform. . c. A person below the platform floating on a rubber raft