Question

A stationary source produces a sound wave at a frequency of 100 Hz. The wave travels at 1125 feet per second. A car is moving toward the sound source at a speed of 100 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 ft; perceived wavelength: 12.25 ft
wavelength of the stationary source: 11.25 ft; perceived wavelength: 12.25 ft

wavelength of the stationary source: 10.25 ft; perceived wavelength: 11.25 ft
wavelength of the stationary source: 10.25 ft; perceived wavelength: 11.25 ft

wavelength of the stationary source: 11.25 ft; perceived wavelength: 10.25 ft
wavelength of the stationary source: 11.25 ft; perceived wavelength: 10.25 ft

wavelength of the stationary source: 12.25 ft; perceived wavelength: 11.25 ft
wavelength of the stationary source: 12.25 ft; perceived wavelength: 11.25 ft

Answer 1

wavelength of the stationary source: 11.25 ft; perceived wavelength: 10.25 ft

Work:
- λ = v/f = 1125/100 = 11.25 ft.
- For the moving observer the perceived wavelength is (1125 − 100)/100 = 10.25 ft (matches the choice).