Problem that (probably) involves Archimedes' principle

[tsw99]

Homework Statement

Serway book 14.26
The weight of a rectangular block is 15N. With a thin string, the center of the horizontal bottom face of the block is tied to the bottom of a beaker partly filled with water. 25% of the block is submerged when the tension is 10N

Oil of density 800 kg/m^3 is steadily added to the beaker and form a layer above the water and surronding the block. The oil exerts forces on each of the four side walls that the oil touches.

Explain what happens to the tension when oil is added?

Homework Equations

The Attempt at a Solution

I suggest the tension will increase by looking at the next question, but I really do not understand why the tension changes by adding oil. Not only the buoyancy changes because it also displaces some oil?

 

[tiny-tim]

hi tsw99!

… I suggest the tension will increase by looking at the next question, but I really do not understand why the tension changes by adding oil. Not only the buoyancy changes because it also displaces some oil?

i assume that the string stays the same length, and the water stays the same volume, so the same amount of the block is "under" water, but some more of the block is now covered by oil

find the buoyancy force before, and the buoyancy force after