there are no molecules in it to vibrate
Answer:
Velocity v= 12.25 
Explanation:
The first rock dropped give the distance Y in meters

Now the motion of the second rock the time change so to know the velocity

The top of the trajectory is the point where it changes from rising to falling. At that exact instant, its vertical speed is zero.
Answer:
hydrometer
Explanation:
A hydrometer is an instrument used to determine specific gravity. It operates based on the Archimedes principle that a solid body displaces its own weight within a liquid in which it floats. Hydrometers can be divided into two general classes: liquids heavier than water and liquids lighter than water.