Question

A body of mass 70kg . when completely immersed in water, displaces 20000 c.c. of water. find :
1) weight of the body in water
2) R D of material of the body​

Answer 1

GiveN:

• Mass of the body, m = 70 kg

• Water displaced by the body = 20000 cm³ = 0.02 m³

I) In order to find the weight of the body in water we can simply equate the mass of solid immersed in water to the mass of water displaced.

That implies,

↬ Mass of solid immersed = Mass of water displaced

But, we know that,

↬ Mass of solid immersed = Density × Volume

Substituting the values,

↬ Mass of solid immersed = 1000 × 0.02

↬ Mass of solid immersed = 20 kg.

$\therefore$ Weight of the body in water is 20 kg.

II) To find the RD (Relative density) we know the direct formula instead of any lengthy methods.

That is,

Relative density = Density in CGS unit. [we've to calculate it in CGS unit]

So,

$\longrightarrow\sf Density = \dfrac{mass}{volume}$

$\longrightarrow\sf Density = \dfrac{70 \times 1000}{20000}$

$\longrightarrow{ \boxed{\sf {Density = 3.5 \: g cm {}^{3} }}}$

$\therefore$ Relative density of the material of the body is 3.5 gcm³