In really stormy weather and with the right conditions, the sky would dump a bunch of hail, making the roads rather hazardous. A choir director was driving his car in these conditions and going a tad fast under the circumstances. His car began to slip on the balls of ice in the road towards two music students walking in front of him, so he leaned on his horn to warn the students to jump out of the way. Since he has career in music, his car horn is set to emit a frequency at exactly Tenor C – 523 Hz. The students have perfect pitch and are able to determine that the frequency that they hear is now 554 Hz (a semitone sharp for any musicians in the room). Since they have also taken Physics with Algebra, they were able to determine the choir director’s speed. What was that speed?

Answer 1

Isn't there a standard formula for doppler , stationary listner, moving source?

Source moving towards observer:

f'=fo(vwave/(vwave-Vs)
and you are looking to compute vs