Question

A body of mass70kg has volume of 20000cm^3.Find weight of body in water?

Answer 1

Volume = 2000 cm3

= 2000 x 10-6 m3

= 2 x 103 x 10-6 m3

= 2 x 10-3 m3

So, density of the substance = 70 kg/ 2 x 10-3 m3

= 35 x 103 kg/m3

Relative density =  density of substance/density of water

= 35 x 103/103

= 35. 

Answer 2

M = 70 kg
V = 20000 cm^3 = 0.02 m^3

Density, D = M/V = 70/0.02 = 3500 kg/m^3

Density of water, d = 1000 kg/m^3

Since the object is denser than water, it will sink.

Apparent weight of object in water = (D - d)Vg = (3500-1000)×0.02×9.8 N = 490 N

Weight of body in water is 490N