[8 pts] On a long trip that you take to forget for a while about physics, you find yourself driving directly towards a vertical canyon wall. You've previously noticed that your car horn has a frequency of 440 Hz. You glance at the speedometer and notice you're moving at 30 km/h. a. What is your horn's frequency as heard by a person standing motionless at the base of the canyon wall? b. What will be the beat frequency that you (in the car) will hear between the car horn's sound and the reflected sound from the wall? (Take the speed of sound in air to be 340 m/s. Be careful in part b) - there are two Doppler shifts)