Question

A dog whistle uses a frequency higher than humans can normally hear. A pet owner wants to test his dog whistle. The owner has a helper drive a car and blow the whistle while he stands on the sidewalk. In which direction should the driver drive so that the pet owner can hear it and why?

Answer 1

He should drive in the opposite direction of the owner.

Step-by-step explanation:

This can be understood by the Doppler Effect. According to this effect the frequency of an approaching wave increase while the frequency of the wave will decrease if it recedes.

For example when you hear a siren of an ambulance, the pitch of the siren increase as it moves towards you because there is an increase in frequency. When the ambulance moves from you the pitch will decrease because the frequency of the sound wave from siren will decrease.

In the given case, to hear the sound of the whistle driver need to move away from it so that the frequency is decreased and he will be able to hear it. So the driver will need to drive in the opposite direction of the owner.

Answer 2

Answer: The driver should drive away from the pet owner.

Explanation:

The apparent frequency reduces when the source and listener are relatively moving away from each other and increases when they are moving towards each other. This from the Doppler's effect. Thus, driver should drive away from the pet owner so that the apparent frequency decreases and can be heard by the pet owner.