Question

A plastic scoop of mass 12g and density 0.6g/cc floats in water. How much mass is put inside the scoop to make it sink?

Answer 1

Buoyancy force acting on the plastic scoop will be given by

$F_b = \rho V g$

volume of the scoop is given by

$V = \frac{m}{\rho} = \frac{12}{0.6} = 20 cc$

now buoyancy force will be

$F_b = 1000 * 20*10^{-6}* 10 = 0.2 N$

now the weight of the plastic scoop

$W = 0.012 * 10 = 0.12 N$

extra mass that we can put inside scoop will be

$W' = F_b - W$

$W' = 0.2 - 0.12 = 0.08 N$

so extra mass that we can put inside the scoop will be

$m = 0.008 kg = 8 gram$

so we have put 8 gram in the scoop