Calculating the Mass of a Hollow Pipe Using Density and Dimensions

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To calculate the mass of a hollow pipe, the outer radius is 4.5 cm, the inner radius is 2.8 cm, and the length is 36 cm, with a density of 7.8 g/cm^3. The correct approach involves calculating the volume of the hollow section by subtracting the inner volume from the outer volume, using the formula for the volume of a cylinder. The mass can then be determined by multiplying the volume by the density and converting the result to kilograms. A misunderstanding arose regarding the addition of the inner and outer radii, which led to an incorrect calculation. The final mass should be accurately computed based on the correct volume formula.
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Homework Statement



A piece of pipe has an outer radius of 4.5cm, an inner radius of 2.8cm and length of 36cm

The density of the pipe is 7.8 g/cm^3

What is the mass of this pipe? Answer is in unites of kg.

Homework Equations



Density=mass/volume

Mass= (density)(volume)

Volume= mass/density

The Attempt at a Solution



I subtracted the volume of the hollow inside of the tube from the large radius (2.8+4.5cm) and multiplied that by the density given. Then I converted to kg by dividing by 1000. My answer came up to be appx 40 kg. But I believe I'm wrong.
 
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movsesinator1 said:
I subtracted the volume of the hollow inside of the tube from the large radius (2.8+4.5cm)...
The outer radius is given as 4.5 cm. (No need to add 2.8+4.5.)
 
Oh yeah thanks.
I thought that i had to add the radii because the diagram on the page made it seem as if the outer radius was that of only the thickness of the pipe.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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