A ball filled with air has a volume of 500 ${{cm}^{3}}$. Calculate the minimum force applied by a child to put it completely inside the water. (Take, g = 10 ${{m}^{-2}}$)

Given that,

Volume, V = 500 ${{cm}^{3}}$

=500 x ${{10}^{-6}}$ ${{m}^{3}}$,

g = 10 ${{ms}^{-2}}$, F = ?

Force required to put the ball inside the water = Buoyant force

= Weight of water displaced = mg … (i)

Now, we know that,

Mass of water = Density of water x Volume m = pV

On substituting this value in Eq. (i) , we get (1/2) Force = pVg

= (1000 ${{kgm}^{-3}}$, ) x (500 x ${{10}^{-6}}$ ${{m}^{3}}$, )x(10${{ms}^{-2}}$, )

= 1000 x 500 x ${{10}^{-6}}$ x 10 N = 5 N

.’. Minimum force applied by a child to put the ball completely inside the water is 5 N.