A train at rest emits a sound at a frequency of 1057 Hz. An observer in a car travels away from the sound source at a speed of 20.6 m/s. What is the frequency heard by the observer

993.52 Hz

Explanation:

The frequency of sound emitted by the stationery train is 1057 Hz.

The car travels away from the train at 20.6 m/s.

The frequency the observer hears is given by the formula:

where v = velocity of sound = 343 m/s

vo = velocity of observer

f = frequency from source

This phenomenon is known as Doppler's effect.

Therefore:

The frequency heard by the observer is 993.52 Hz.