Explain the conditions in which a person can or can’t hear an echo. Which of the following materials would be the least efficient in soundproofing a room: clay tile, plaster, or perforated acoustic ceiling material? Be sure to use your knowledge of the coefficient of absorption in your explanation. Compare and contrast infrasonic and ultrasonic vibrations. Describe the responses of the human ear to sound waves coming from the right side, left side, or in phase.

for someone to be able to hear an echo the following conditions must be true:

-the minimum distance between the sound and reflector in the air must be 17 meters, however this does vary depending on the speed of sound in the medium.

-the sound must be intense enough so that it could reach the ear and be audible

-the reflectors size must be large enough compared to the Sound wavelength

Explanation:

a lot of it means it can be "burned" for energy and sold at one price. if it is scarce, the price will go up

a.   mass number from atomic number