Question

A ball weighs 80g in air, 60g in water and 50g in liquid. If the density of water is 1g/cm^3 , find the density of the liquid.

Answer 1

Relative density = original weight/weight loss
therefore
density of object/density of water = weight in air/(weight in air-weight in water)

density of object/density of liquid = weight in air/(weight in air-weight in liquid)

so,
density of liquid/density of water = (weight in air-weight in liquid)/(weight in air-weight in water)

density of liquid/1 =80-50/(80-60) = 3/2
density of liquid = 1.5

OR

When the ball is immersed in water, it displaces some amount of water which is
(80 - 60) = 20g
Density of water = 1 g cm^-3
Volume of ball = Volume of water it displaces
= mass/density
= 20g/ 1 = 20 cm^3

Density of ball = Mass/Volume
= 80/20 = 4 g cm^-3

When immersed in liquid
the ball displaces 80-50 = 30g of liquid
So density of liquid =
Mass/volume =
30/20 = 1.5 g cm^-3

Hence, density of liquid = 1.5 g cm^-3