Mass of body = 70 kg
Volume of water displaced = 20,000 cm3 = 0.02 m3
(i) Mass of body immersed in water = mass of the water displaced
= volume of water displaced × density of water
= 0.02 × 1000
= 20 kg
Weight of the body = mg = 70 × g = 70 kgf
Weight of water displaced = mg = 20 × g = 20 kgf
Weight of body in water = weight of body in air – upthrust due to liquid
= 70 kgf – 20 kgf [∵ upthrust is equal to the weight of water displaced]
= 50 kgf
(ii) Density = Mass\over Volume
= 70\over 0.02 = 3500 kg m-3
RD of body = 3500\over 1000 = 3.5
Therefore,
Relative density of body = 3.5