Awhistle you use to call your hunting dog has a frequency of 21 khz, but your dog is ignoring it. you suspect the whistle may not be working, but you can't hear sounds above 20 khz. to test it, you ask a friend to blow the whistle and hop on his moped. in which direction should he ride (toward or away from you) to know if the whistle is working? explain in words or with a diagram