Question

A certain body weighs 12N in air and 10 N in when immersed in water. Find its

total volume and its density.

Answer 1

The weight of body in water

$$W=mg-g\rho_wV$$

Hence, the volume of a body

$$V=\frac{mg-W}{g\rho_w}=\frac{12-10}{9.8*1000}=2*10^{-4}\:\rm m^3$$

The density of a body

$$\rho=\frac{m}{V}=\frac{12}{9.8*2*10^{-4}}=6000\:\rm kg /m^3$$