A van is approaching a stationary motion detector at 45 m/s. The motion detector
ID: 2244283 • Letter: A
Question
A van is approaching a stationary motion detector at 45 m/s. The motion detector emits ultrasonic sound wavestoward the van, which then reflect off the van and are received by the motion detector. If the frequency of the emitted sound waves is 0.150 MHz, what is the frequency of the reflected sound measured by the detector? A van is approaching a stationary motion detector at 45 m/s. The motion detector emits ultrasonic sound waves
toward the van, which then reflect off the van and are received by the motion detector. If the frequency of the emitted sound waves is 0.150 MHz, what is the frequency of the reflected sound measured by the detector?
Explanation / Answer
the van hears
f = (343+45)/343*0.15=0.17 MHz
so the detector hears
f = 343/(343-45) *0.17=0.196 MHz