N A siren emits a sound of frequency 1.44 × 103 Hz when it is stationary with respect to an observer. The siren is moving away from a person and toward a cliff at a speed of 15 m/s. Both the cliff and the observer are at rest. Assume the speed of sound in air is 343 m/s. What is the frequency of the sound that the person will hear a. coming directly from the siren and b. reflected from the cliff?