Question

A stationary source produces a sound wave at a frequency of 100 Hz. The wave travels at 925 feet per second. A car is moving toward the source at a speed of 25 feet per second.

What is the wavelength of the stationary sound source and the wavelength that a person in the car perceives?

(1 point)
Responses

wavelength of the stationary source: 11.25 perceived wavelength: 13.25 ft
wavelength of the stationary source: 11.25 perceived wavelength: 13.25 ft

wavelength of the stationary source: 10.25 perceived wavelength: 9.50 ft
wavelength of the stationary source: 10.25 perceived wavelength: 9.50 ft

wavelength of the stationary source: 11.25 perceived wavelength: 9.25 ft
wavelength of the stationary source: 11.25 perceived wavelength: 9.25 ft

wavelength of the stationary source: 9.25 perceived wavelength: 9.00 ft
wavelength of the stationary source: 9.25 perceived wavelength: 9.00 ft

Answer 1

Stationary wavelength: λ = v/f = 925/100 = 9.25 ft.

Observer moving toward source: f' = (v + v_o)/v * f = (925+25)/925 * 100 ≈ 102.703 Hz,
so perceived wavelength λ' = v/f' ≈ 925/102.703 ≈ 9.00 ft.

Answer: wavelength of stationary source = 9.25 ft; perceived wavelength ≈ 9.00 ft.