Adog whistle uses a frequency higher than humans can normally hear. a pet owner wants to test his dog whistle. the owner has a 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?

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.

explanation:

as the height from which the ruler was dropped increased, the speed of the ruler at ryan's hand increased.

probably not if net force is zero