first figure out what higher frequency the wall hears
that frequency emmitted from the wall toward the car at that frequency
then get the still higher frequency back at the car
A police car siren emits a sound wave with a frequency fs = 400 Hz and it is moving toward the wall at 25 /m/s. What frequency reflected from the wall does the driver of the police car hear ?
The speed of sound is 340 m/s.
2 answers
fi=f(v)/(v-vs)
fi=400(340m/s)/(340m/s-25)
fi=431.7Hz
fi=400(340m/s)/(340m/s-25)
fi=431.7Hz