Answer:
7.5 cm
Explanation:
In the figure we can see a sketch of the problem. We know that at the bottom of the U-shaped tube the pressure is equal in both branches. Defining 
Ethyl alcohol density and 
Glycerin density , we can write:
Simplifying:
On the other hand:
Rearranging:
Replacing (2) in (1):
Rearranging:
Data:
The velocity of the mass after 9 second is 88 m/s
All that business about the crane and the rope and the falling
is only there to confuse us.
The piano ended up 5 meters above the ground.
Potential energy = (mass) (gravity) (height)
= (200 kg) (9.81 m/s²) (5 m)
= (200 · 9.81 · 5) (kg-m²/s²)
= 9,810 joules .
