Question

A solid weighs 80g in air and 64g in water .calculate the relative density of solid. State if object would sink or float if kept in water

Answer 1

relative density = weight in air / weight in air -weight in water

R.D = 80/80-64
R.D = 80/16 
R.D = 5
now,
density of water = 1 g/cm³
so the object would sink .

i hope it helps.............. 

Answer 2

According to Archimedes principle,
Upthrust = Weight of liquid displaced
Weight of water displaced = 80-64 = 16

Now, density of water = 1g/cm³
1 g/cm³ = 16 g / x cm³
Therefore, volume of water displaced =
x = 16 cm³

So, volume of the solid = 16 cm³

It density = Mass/volume = 80/16 = 5 g/cm³

Relative density = Density of solid /Density of water = 5/1 = 5

Now, since the solid's density is more than water, it will sink in water.