You are provided with a hollow iron ball A of volume 15 cm3 and mass 12 g and a solid iron ball B of mass 12 g. Both are placed on the surface of water contained in a large tub. (a) Find upthrust on each ball. (b) Which ball will sink ? Give reason for your answer. ( Density of iron = 8.0 g cm-3)

(a) Mass of ball A = 12 g

Mass of ball B = 12 g

The volume of the hollow iron ball A = 15 cm³

Density of iron = 8 g cm^–3

The volume of the hollow iron ball B = 12/8 = 1.5 cm^–3

Upthrut on ball A = 15 × 1 × g = 15 gf

Upthrut on ball B = 1.5 × 1 × g = 1.5 gf

(b) Solid iron ball B will sink.

Ball B experiences an upthrust of 1.5 gf in water which is less than its weight of 12 gf. Hence ball B will sink. Ball A experiences an upthrust of 15 gf that is greater than its weight of 12 gf. Hence it will float with that much part submerged for which upthrust becomes equal to its weight of 12 gf.