Question Detail
Question
The frequency of a car horn is 400 Hz. What frequency is observed if the car moves with speed 30 m/s toward a stationary receiver? Take velocity of sound in air to be 340 m/s.
Correct Answer
Option B is the correct answer.
Detailed Explanation
For a moving source and stationary observer, the observed frequency is f' = f * v / (v - v_s). Here f = 400 Hz, v = 340 m/s, v_s = 30 m/s. f' = 400 * 340 / (340 - 30) = 400 * 340 / 310 = 438.7 Hz ≈ 439 Hz.
Hint
Use the Doppler effect formula for a moving source.