Question

a brick with specific gravity of 3.5 weights 2 kg in water, how much it weights in air

Answer 1

Let the weight of brick in air = X

Weight difference in air and in water = X -2

Buoyant force of water = X - 2

Buoyant Force in water = density of water x g x volume of brick

X - 2 = 1000 kg/m3 * 9.81 m/s2 * V

V = (X-2)/(9.81*1000)

Weight of brick in air = X

Mass of brick = X/9.81

Density of brick = mass / volume

= (X/9.81) / (X-2 / 9.81*1000)

= (1000X)/(X-2)

Specific gravity of brick = density of brick / density of water

3.5 = (1000X)/(X-2) / (1000)

3.5*1000 (X - 2) = 1000X

3.5X - 7 = X

2.5X = 7

X = 2.8 kg