What is the frequency does a stationary observer hear when a train approaches her with a speed of 30 m/s. The frequency of the train horn is 0.600 kHz and the speed of sound is 340 m/s.
A) 551 Hz
B) 653 Hz
C) 600 Hz
D) 658 Hz

Question

Quizplus · Accepted Answer

The frequency heard by a stationary observer when a source approaches is given by the formula $f' = f \left(\frac{v + v_o}{v - v_s}\right)$, where $f'$ is the observed frequency, $f$ is the source frequency, $v$ is the speed of sound, $v_o$ is the observer's speed (0 m/s in this case since the observer is stationary), and $v_s$ is the speed of the source. Plugging in the given values: $f' = 0.600 \times 10^3 \left(\frac{340}{340 - 30}\right) = 0.600 \times 10^3 \left(\frac{340}{310}\right) = 658 Hz.$

What Is the Frequency Does a Stationary Observer Hear When