Question

A rubber ball floats on water with its 1/3^rd volume outside water. What is the density of rubber? 

Answer 1

Let the volume of the ball be V .

Volume of ball above the surface of water = ${\displaystyle \frac{1}{3}}$V

∴ Volume of ball immersed in water = ${\displaystyle \text{V}-\frac{1}{3}\text{V}=\frac{2}{3}\text{V}}$

By the principle of floatation on,

${\displaystyle \frac{\text{Volume of rubber ball immersed}}{\text{Total volume of rubber ball}}=\frac{\text{Density of rubber}}{\text{Density of water}}}$

or , ${\displaystyle \frac{2}{3}=\frac{\text{Density of rubber}}{1000}}$

or , Density of rubber ball = ${\displaystyle 1000\times \frac{2}{3}=666.7 {\text{kgm}}^3\approx 667 {\text{kgm}}^3}$