an object weighs 40N in air, weighs 20N when submerged jn water and 30N submerged in a liquid of unknown density. what is the density of the liquid?

502.51 kg/m^3

Explanation:

Upthrust on object in water is 40 - 20 = 20 N

Upthrust is equal to the buoyancy forces given as

B = pgv

p is density of water 1000 kg/m^3

g = acceleration due to gravity 9.81 m/s^2

v is the volume of liquid displaced.

Therefore

B = 1000 x 9.81 x v

20 = 9810v

v = 2.038x10^-3 m^3

For Upthrust in unknown liquid, we have 40 - 30 = 10 N

Bouyancy force for the liquid will be

B = P x 9.81 x 2.038x10^-3

NB - the same volume of fluid will be displaced i. e 2.038x10^-3 m^3

Equating we have

10 = P x 9.81 x 2.038x10^-3

10 = 0.0199p

p = 10/0.0199 = 502.51 kg/m^3