what is the minimum riding speed needed to be able to hear the whistle? Remember, you can assume the following things: The whistle you use to call your hunting dog has a frequency of 21.0 kHz, but your dog is ignoring it. You suspect the whistle may not be working, but you can't hear sounds above 20.0 kHz. The speed of sound is 330m/s at the current air temperature.
Are you riding away from a reflecting surface and listening for the echo? If so, use the appropriate Doppler shift formula, with a received frequency of 20 kHz. Let the speed of sound be a.
The answer will be approximately
2 V/a = 1.0kHz /20 kHz = 0.05
V = (1/2)*0.05*330 = 33 m/s = 118 km/h = 74 mph
posted by drwls