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

Let,

V = total volume of rubber ball

ρ = density of the rubber ball

Given,

$\dfrac{1}{3}$rd of V is outside water

Therefore, volume inside water

= V - $\dfrac{1}{3}$V

= $\dfrac{2}{3}$V

By the principle of flotation,

Weight of ball = Weight of water displaced by the immersed part of the ball.

and density of water = 1000 kg m^-3

i.e., V x ρ x g = $\dfrac{2}{3}$ V x 1000 x g

Hence,

ρ = $\dfrac{2000}{3}$ = 667 kg m^-3

Hence,

Density of rubber = 667 kg m^-3