Question

Question 1: High frequency whistles are often used for training dogs and have a frequency of 21 kHz. Stanley’s dog is not responding to the whistle he bought and suspects the whistle may not be working. However, it is difficult for Stan to tell if the whistle is working because humans cannot hear sounds above 20 kHz. In order to test the whistle, he asks a friend to blow the whistle and hop on his four-wheeler. In which direction should his friend ride (toward or away from Stanley) to know if the whistle is working? Explain using words or a diagram.

Going back to the dog whistle in question 1, what is the minimum riding speed needed to be able to hear the whistle (in m/s and miles per hour)? Remember, you can assume the following things: The whistle has a frequency of 21.0 kHz, but Stanley’s dog is ignoring it. He suspects the whistle may not be working, but humans can't hear sounds above 20.0 kHz. The speed of sound is 330m/s at the current air temperature.

Step 1: List the givens and unknown quantity

Step 2: Write the equations that will relate the quantities. Manipulate them if necessary.

Step 3: Show all work needed to find the solution.

If the four-wheeler has a top speed of 25 mph, will Stanley and his friend be able to use this method to determine if the whistle is functioning?
     

Answer 1