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# Archimede principle

A polythene rod of length 0.5 m floats upright in water.

a) Given that the densities of polythene and water are 920 and 1000 kg/m3 respectively, what is the length of the rod immersed in water?

b) If the rod floats in another liquid with 0.4 m of its length under the liquid surface, what is the density of the liquid?

### 1 Answer

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- 天同Lv 77 years agoFavorite Answer
(a) Let L be the length of rod immersed in water

Upthrust = weight of water displaced = L.A.(1000)g

where A is the cross-sectional area of rod and g is the acceleration due to gravity

Since weight of rod = (0.5A).(920g)

thus, 0.5A.(920g) = LA(1000g)

L = 0.46 m

(b) Using the above equation, but substitute L = 0.4 m and density of water by density of liquid p, we have,

0.5A(920g) = 0.4A(pg)

i.e. p = 1150 kg/m^3

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