Question

A body weights 40g in air. If its volume is 10cc,in water,its weight becomes?

Answer 1

By using Archimedes's theorem,

Loss of weight = Buoyant force

                        = weight of the water displaced by the body

                        = mg [m=mass of the body, g= acceleration due to gravity]

                       = Vdg [ V = Volume of the body, d = density of water]

                       = 10 cm³ X (1 g/cm³) X g [density of the water = 1g/cm³]

                       = 10g grams

weight of the body in air = 40g grams

Therefore, weight of the body in water = weight in air - loss of weight

                                                                 = 40g -10g

                                                                 = 30g

Answer 2

According to Archimedes principle

Mass in air - 40 gm

Vol. = 10 cm cube

So it when immersed in water displaces 10 grams of water. Therefore it also experiences 10N of buoyant force. Hence it loses 10 grams of its mass.

So, mass in water is equal to, mass in air-weight loss

40-10=30gms

Final answer =30 gms