Question

A block of wood of volume 25 cm³ floats in water with 20 cm³ of its volume immersed in water.
Calculate:
(1) density of wood
(2) the weight of block of wood.

Answer 1

Volume of wooden block = V = 25 cm³

Volume of wooden block immersed in water = 20 cm³

Volume of water displaced by wooden block=volume of wooden

block immersed in water = 20 cm³

Density of water = ρ_water = 1 gcm^-3

Density of wooden block =ρ_wood = ?

By law of floatation:

volume of wooden block x Density of wood=Volume of water displaced x Density of water

`25 xx rho_"wood" = 20 xx 1`

`rho_"wood" = 20/25 = 0.8` g cm^-3 

Weight of wooden block `"V"rho_"wood""g"`

= 25 × 0.8 × g = 20 gf