1. A friend of yours is loudly singing a single note at 400 Hz while driving toward you at 25.0 m/s on a day when the speed of sound is 340 m/s. a. What frequency do you hear? b. What frequency does your friend hear if you suddenly start singing at 400 Hz? c. Once your friend reaches you, and you are next to each other (essentially at the same location) and not moving, your friend sings 400 Hz. You are also singing. If you hear 3 beats per second, what frequency are you singing?