Question

a ball filled with air has a volume of 500 cm cube. calculate the minimum force applied by a child to put it completely inside the water . ( take g is equal to 10 m /s square)

Answer 1

Answer:

The buoyant forces acting on submerged objects are equal to the weight of the water displaces. The weight of the displaced water, in turn, is directly proportional to the volume of the submerged object.

Then,

The ball with air filled is completely submerged, this is also the volume of water displaced, i.e. Vw . Now, find the mass of water displaced from the relationship between its volume and density, both of which are known.

Given value:

Volume, V = 500 cm3

m =  ρ x V

m = 1.000×103 kg/m3 x 0.00050 m3
m = 0.50 Kg

By Archimedes’ principle, the weight of water displaced is mg , so the buoyant force is:

Buoyant Forec, F = m x g
= 0.50 x 10  (g = 10)
F = 5 N

Answer 2

volume of balloon (v)= 500cm³ 
If it is completely immersed in water, it will displace the same volume water.
So buoyant force would act on it in the upward direction.The child need to apply same amount of force as buoyant force to put it inside.

density of water = 1 g/cm³


So the child needs to apply 5N force to put it completely inside water.

(Note: The density of air is negligible compared t density of water. So you should ignore the mass of air.)