Asound wave traveling downward with a speed of about 4,000 m/s suddenly slows to 1,500 m/s not far below the earth’s surface. what has the sound wave most likely encountered? a different kind of rock an underground lake an open cavity a pile of dinosaur bones

Explanation:

In general, sound (mechanical waves) travels faster in solids than in liquids, and faster in liquids than in gases. This is because the speed of the mechanical waves is determined by a relationship between the elastic properties of the medium in which they are propagated and the mass per unit volume of the medium (that is:density).

In other words: The speed of sound varies depending on the medium through which the sound waves travel.

So, if we are told the sound wave initially had a speed of 4,000 m/s and it suddenly decreases to 1,500 m/s, this means the sound waves passed from a solid medium to a liquid medium.

Hence, the correct option is: an underground lake.