# Hollow sphere in water

## Homework Statement

Hollow iron sphere is half submerged in water.Sphere has outer diameter of 10 cm. Calculate thickness of the wall , when the iron density is 7.9 g / m3.
I get answer 0.11cm, book says that it is 0.22cm.

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## The Attempt at a Solution

First i found buoyant force F=ρgV/2 where ρ is density of water and V is volume of a sphere.
Then I found mass of a sphere : ρgV/2=mg
m=0.26 kg
I know density of iron ,so: 7900=0.26/v where v is volume of the wall
(v= volume of outside sphere - volume of inside sphere.)
From there I get thikness of the wall to be 0.11cm.

## Answers and Replies

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Bystander
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half submerged in water.

TSny
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I get answer 0.11cm, book says that it is 0.22cm.
Your method looks correct. I agree with your answer of .11 cm.

Bystander
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Someone made my "intuitive" error while re-writing the exercise for the "n-th" edition; agreed, 0.11 cm.