Question

noah and nina are 15 m apart in a closed room. noah says the same sentence twice. the first time, nina does not hear the sound, but she does hear the sentence the second time. what best describes the difference between the second sound wave and the first? the second sound wave reflects off the walls of the room, so nina is able to hear the sound. the second sound wave travels faster to nina, so less energy is dissipated through the air. the air molecules in the compressions of the second wave are more dense, so the sound is louder. the air molecules in the second wave are spaced evenly, so a high - frequency wave is produced.

Explanation:

Sound waves can reflect off surfaces. In a closed room, the first sound wave might not reach Nina directly (maybe blocked or too weak). But the second - time, the sound wave reflects off the walls (a property of sound wave reflection). This reflection allows the sound to reach Nina.

• Sound travels at a constant speed in a given medium (air in the room), so the second option about speed is wrong.
• There's no indication that the air molecules' density in compressions changed for the second wave (so the third option is incorrect).
• Sound wave frequency is determined by the source (Noah's voice), not by how air molecules are spaced (so the fourth option is wrong).

Answer:

The second sound wave reflects off the walls of the room, so Nina is able to hear the sound.