# Pressure, Buoyant Force problem

• ChunkymonkeyI
In summary, the conversation discusses finding the density of an unknown material by determining the percentage of its volume in the water. The equations used are density=m/v, F=mg, Fb=density of fluid times volume of the fluid times g, and P=density times height times g. The solution involves finding the buoyant force, using F=PA and F=mg, and calculating the percentage of the object's volume in the fluid. The final answer should be 750 kg/m^3 instead of 7.5 kg/m^3.

## Homework Statement

A solid cube of unkown material is floating upright in water so that 1/4 of the cube is above the surface of the water. What is the density of the material?

## Homework Equations

Density=m/v
F=mg
Fb=density of fluid times volume of the fluid times g
P=density times height times g

## The Attempt at a Solution

Since the cube is floating upright in the water I think that means that the force of weight is equal to the buoyant force.
P=density times h times g
P=1000 kg/m^3 times 1/4 times 9.80 which equals 2450 Pa
Then I used F=PA
F=2450 Pa times 1/4 which equals 612.5 N
Then I used F=mg
m=F/g
m=612.5 N/9.80 m/s^2
m=62.5 kg
I don't know what 2 do from there and I think one of my step is wrong because I multiplied the area by 1/4 but I don't think that's right can someone please help me and explain 2 me how to solve this problem

(Density of the object / density of the fluid) x 100 = Prencentage of object's volume in the fluid

But when I do that I get the following:
b/1000 kg/m^3 times 100=3/4
100b/1000=3/4
1b/10=3/4
b=7.5 and b is the density of the object but on my sheet it says the answer is 750 kg/m^3 and its almost like my answer but the decimal is moved over and idk y. Maybe my work was wrong or something can u explain ?

hmzone said:
(Density of the object / density of the fluid) x 100 = Prencentage of object's volume in the fluid

But when I do that I get the following:
b/1000 kg/m^3 times 100=3/4
100b/1000=3/4
1b/10=3/4
b=7.5 and b is the density of the object but on my sheet it says the answer is 750 kg/m^3 and its almost like my answer but the decimal is moved over and idk y. Maybe my work was wrong or something can u explain ?

3/4=0.75 is not the Precentage dude, it's 75%