Tomato, Salt water and Olive oil

[huybinhs]

Homework Statement

You put a tomato into a vessel of salty water - it floats. Now you pour olive oil into the same vessel. Which one of the following statements is true?
a)Less of the tomato will be above the surface of the water.
b) The tomato will stay at the same height.
c) More of the tomato will be above the surface of the water.

2.The salty water has a density of 1040 kg/m3 and the tomato a density of 980 kg/m3. Before you pour in the olive oil, what percentage of the tomato floats above the surface of the water?

3.After you pour in enough olive oil (density of 920 kg/m3) so that the top of the tomato is completely covered, what percentage of the tomato floats above the surface of the water?

2. The attempt at a solution

1.Olive oil floats on water, therefore it has a lower density. That means the difference between that density and that of the tomato is less, so a will be the choice. Correct?

2. I tool 980/1040 and * 100 to get the percentage but INCORRECT.

3. I did the second wrong, so I have no clue.

Please advise! Thanks!

 

[willem2]

question 1
They meant above of the surface of the water, not above the surface of the olive oil.
There's layer of oil on top of the water, not an oil-water mixture.
The buoyant force is equal to the weight of the displaced water + the weight of the displaced oil. There's now some displaced oil, so there has to be less water displaced

question 2. You calculated the percentage that's under water.

 

[huybinhs]

question 1
They meant above of the surface of the water, not above the surface of the olive oil.
There's layer of oil on top of the water, not an oil-water mixture.
The buoyant force is equal to the weight of the displaced water + the weight of the displaced oil. There's now some displaced oil, so there has to be less water displaced

question 2. You calculated the percentage that's under water.

So, it will be c then => Correct

Second part:

100 - that number = correct.

Thanks so much! I got it all right ;)