Question

A ping-pong ball has a volume of 3 x10^-5 m^3 and density of 84 kg/m^3. What force is required to hold it completely submerged under water ? Take, density of water = 1000 kg/m^3;g= 10 m/s^2.​

Answer 1

Answer:

0.2748 N

Explanation:

Volume of the ball $V=3\times 10^{-5}$ m³

Density of the ball $d=84$ kg/m³

Mass of the ball

$M=V\times d$

$\implies M=84\times 3\times 10^{-5}$ kg

$\implies M=2.52\times 10^{-3}$ kg

Thus weight of the ball

$W=Mg$

$\implies W=2.52\times 10^{-3}\times 10$ N

$\implies W=0.0252$ N

When the ball is completely submerged in water, it will replace water equal to its volume

The weight of this water will be equal to the bouyant force upwards

Thus, the bouyant force

$F_b=3\times 10^{-5}\times 1000\times 10$ N

$\implies F_b=0.3$ N

The force required to hold it completely under water

$=F_b-W$

$=0.3-0.0252$ N

$=0.2748$ N

Hope this helps.