Question

A body is submerged in water. It is taken out and then submerged in mercury. What happens to its relative density with respect to the liquid in which it is submerged?
A) Increases
B) Decreases
C) Remains constant
D) Can’t say

Answer 1

Hint: Density of a substance is defined as the amount of mass in a unit volume of matter. Relative density is defined as the ratio of the density of a substance to the density of some reference substance. Relative density is a dimensionless quantity.

Complete step by step answer:
Step I:
Given here are two liquids whose relative densities are to be compared. One liquid given is water and the other is mercury. Let the relative density of water is ${\rho _1}$ and the relative density of mercury be ${\rho _2}$.
Step II:
Formula for relative density is written as
${\rho _r} = \dfrac{{{\rho _1}}}{{{\rho _2}}}$
Relative density of water is$ = 1000kg/{m^3}$
Relative density of mercury is$ = 13560kg/{m^3}$
The density of mercury is greater than the density of water. But the relative density of mercury is less than that of the relative density of water.
Step III:
It is clear that mercury has a density of $13.5$ of that of water. Therefore, mercury is denser than water.
Step IV:
Therefore, if the body is first submerged in water and then submerged in mercury, then its relative density will decrease.
Option B is the right answer.

Note: It is to be noted that the terms relative density and specific gravity are not the same. Specific gravity is a special case of relative density. Specific gravity of a substance determines whether any object will float or sink. It is the density of an object with respect to water. If the density is less than $1$ then the object will float in water. If the density is greater than $1$ the object will sink.