A train traveling at 82.8 kilometers per hour is blowing its horn as it approaches you. The horn has a frequency of 312 Hz. Assume the speed of the sound is 331 m/s. What is the observed frequency of the horn?
335 Hz
312 Hz
292 Hz
412 Hz
To calculate this, we will use the following formula: f₀ = f × v ÷ (v - v₁) where: f₀ - frequency heard f - actual frequency v - speed of sound v₁ - speed of source
We know: f = 312 Hz v = 331 m/s v₁ = 82.8 km/h = 23 m/s
We need: f₀ = ?
f₀ = f × v ÷ (v - v₁) ⇒ f₀ = 312 Hz x 331 m/s ÷ (331 m/s - 23 m/s) ⇒ f₀ = 312 Hz × 331 m/s ÷ 308 m/s ⇒ f₀ = 335.3 Hz ≈ 335 Hz
