Question Detail
Question
The horn of a stationary car has a frequency of 400 Hz. What frequency is observed by a receiver moving toward the car at 30 m/s?
Correct Answer
Option A is the correct answer.
Detailed Explanation
For a moving observer and stationary source: f' = f (v + v₀)/v. v = 340 m/s, v₀ = 30 m/s. f' = 400 × (340 + 30)/340 = 400 × 370/340 = 400 × 1.0882 = 435.3 Hz ≈ 435 Hz.
Hint
Use the Doppler effect formula for a moving observer.