1. A whistle with the frequency 400 Hz moves at a speed 20 m/s in a horizontal circle at the end of a rotating string. Find:

a. the highest frequency heard by a person riding a bicycle at a speed 10 m/s toward the whistle.

b. the lowest frequency heard by that person.

2. A bat emits short pulses of sound at a frequency of 3.9 x 10^5 Hz. As the bat swoops toward a flat wall at a speed of 30 m/s, this sound is reflected from the wall back to the bat.

a. What is the frequency of sound incident on the wall?

b. What frequency of sound does the bat hear coming from the wall? Consider the wall as a sound source at the frequency calculated in part (a).