# Physics Problem: what % barrel floating above water

• Nov 20th 2011, 03:07 PM
over9000
Physics Problem: what % barrel floating above water
A solid cylinder (radius 0.150m height 0.120m) has a mass of 7 kg. The cylinder is floating on water, but oil (r=875kg/m^3) is added to the container, the cylinder gets covered by the oil. What % of the cylinder is above water?

I think that that 100% of the solid cylinder is floating above water because the cylinder is less dense than the water and the oil. density_cylinder = (mass_cylinder) / (pi*(radius^2)*h) = (7) / (pi*(0.15^2)(0.120) = 825.248kg/m^3

However, I can't believe the problem is that easy. I must be doing something wrong.
• Nov 20th 2011, 11:16 PM
CaptainBlack
Re: Physics Problem: what % barrel floating above water
Quote:

Originally Posted by over9000
A solid cylinder (radius 0.150m height 0.120m) has a mass of 7 kg. The cylinder is floating on water, but oil (r=875kg/m^3) is added to the container, the cylinder gets covered by the oil. What % of the cylinder is above water?

I think that that 100% of the solid cylinder is floating above water because the cylinder is less dense than the water and the oil. density_cylinder = (mass_cylinder) / (pi*(radius^2)*h) = (7) / (pi*(0.15^2)(0.120) = 825.248kg/m^3

However, I can't believe the problem is that easy. I must be doing something wrong.

It floats so that the sum of the buoyancy forces from the parts in water and oil sum to the weight (in air) of the cylinder.

CB
• Nov 21st 2011, 11:20 AM
over9000
Re: Physics Problem: what % barrel floating above water
I've talked to about 4 other people about this problem. I even talked to a chemistry professor at my college and he agrees that 100% of the cylinder is above the water. I just talked to a physics tutor about this problem and he too agreed that the cylinder is above the water and floating on top of the oil. I still think this problem is too easy.
• Nov 21st 2011, 11:48 AM
CaptainBlack
Re: Physics Problem: what % barrel floating above water
Quote:

Originally Posted by over9000
I've talked to about 4 other people about this problem. I even talked to a chemistry professor at my college and he agrees that 100% of the cylinder is above the water. I just talked to a physics tutor about this problem and he too agreed that the cylinder is above the water and floating on top of the oil. I still think this problem is too easy.

There is probably a typo since you cannot cover the cylinder with oil if it is less dense than the oil.

CB