Question

a solid weight's 120gf in air and 100gf when it is completely immersed in water.find the relative density of the material​

Answer 1

Answer:

Relative density of material is 8.

Explanation:

The solid apparently weighs less in water when compared to air because of the upward buoyant force acting on it when it is submerged in water.  

According to Archimedes principle, the buoyant force acting on an object is equal to the weight of the fluid displaced by it.  

Therefore, the apparent decrease in the weight of an object is equal to the weight of the fluid displaced by it.

Weight of displaced water = Apparent decrease in weight = 120−105=15 gf

Mass of displaced water = 15 g

Volume of solid = volume of water displaced = $\frac{mass}{density}$ = $\frac{15g}{1g/cm^3}$

Actual weight of solid = weight of solid in air =120 gf (since buoyant force due to air is negligible)

Mass of solid = 120 g

Density of solid = $\frac{Mass}{Volume}$ = $\frac{120}{15}$ = 8g/cm³

Relative density of solid = $\frac{Density^s^o^l^i^d}{Density^w^a^t^e^r} = \frac{8g/cm^3}{1g/cm^3} = 8$