Question

which choice best describes when a sonic boom occurs?

when an object travels above the speed of sound and the sound waves are compressed together
when an object travels above the speed of sound and the sound waves are spaced apart
when an object travels below the speed of sound and the sound waves are spaced apart
when an object travels below the speed of sound and sound waves are compressed together

Explanation:

A sonic boom forms when an object moves faster than the speed of sound. As it does so, the sound waves it emits cannot propagate ahead of it, so they pile up (compress) into a single shock wave that creates the boom. Objects moving below the speed of sound do not produce this compressed shock wave.

Answer:

when an object travels above the speed of sound and the sound waves are compressed together