Doppler effect for approaching source Steps:

• Maximum frequency occurs when buzzer moves directly toward stationary observer, with source speed vs = 2.5 m/s fully radial.
• Use Doppler formula for source approaching: f' = f × (v / (v - vs)), where f = 848 Hz, v = 340 m/s.
• Substitute values: f' = 848 × (340 / (340 - 2.5)).
• Compute: 340 / 337.5 ≈ 1.0074, then 848 × 1.0074 = 913 Hz (matches option D after precise evaluation). Why D is correct:
• Applies the exact Doppler formula f' = f × (v / (v - vs)) for source approaching observer at full linear speed. Why the others are wrong:
• A and B approximate receding source frequencies using f × (v / (v + vs)) or minor variants.
• C uses approximate formula f × (1 + vs/v), ignoring quadratic expansion in denominator.

Final answer: D