Doppler effect for moving source Steps:

• Maximum frequency occurs when loudspeaker moves directly toward observer at vs = 15 m/s.
• Apply formula f' = f × v / (v - vs), with f = 2000 Hz, f' = 2007 Hz.
• Substitute: 2007 = 2000 × v / (v - 15).
• Solve: v = [15 × 2007] / (2007 - 2000) = 324 m s^{-1}. Why C is correct:
• Doppler formula directly computes speed of sound as 324 m s^{-1} using given values. Why the others are wrong:
• A: Yields f' ≈ 2114 Hz, exceeding observed shift.
• B: Yields f' ≈ 2105 Hz, exceeding observed shift.
• D: Yields f' ≈ 2090 Hz, under observed shift.

Final answer: C