Please Help!
Sound waves are traveling through the air. Every ½ second, the sound waves pass a detector. Which of the following choices correctly describes the period and frequency of these waves?

The period is 2 s, and the frequency is 2 Hz.
The frequency is ½ second, and the period is 2 Hz.
The period is ½ second and the frequency is ½ Hz.
The period is ½ second, and the frequency is 2 Hz.

Please Help!

Which explanation describes the forces involved for a person to walk down the sidewalk? a. the person's feet push backward on the sidewalk; the sidewalk pushes backward on the person. b. the person's feet push forward on the sidewalk; the sidewalk does not push on the person. c. the person's feet push backward on the sidewalk; the sidewalk pushes forward on the person. d. the person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.

Awave is produced in a rope. the wave has a speed of 33 m/s and a frequency of 22 hz.

Which diagram correctly demonstrates the various forces acting on a ball moving horizontally with some speed?