Question

A person with very good musical pitch listens to a guitarist on a moving stage play a high A (880 Hz) while the stage is moving away at 4.0 m/s on a cold day, 0 °C. What frequency does this person hear? If they can discriminate 0.25 Hz can they tell the difference between this note from a moving guitarist and a stationary guitarist?

Answer 1

The equation to solve this is the relation between speed and frequency

`v=f\lambda`

In this case, we don't know the value of lambda but we are not going to need it, because we are comparing the same wave

For this, we want to know if the 4m/s is higher than 0.25Hz or not to know if the change can be idenfified. Lets remember the speed of sound is 344m/s

`\begin{gathered} 344m/s=880Hz\cdot\lambda \\ \lambda=0.39m \end{gathered}`
`\begin{gathered} 4m/s=f\cdot0.39m \\ f=10.23Hz \end{gathered}`

Based on the frequency found, the change can be identified because is higher than 0.25Hz