Question

A ball weighing $4$ kg of density $4000$ kg $m^{-3}$ is completely immersed in water of density $1000$ kg $m^{-3}$. Find the force of buoyancy on it. $($ Given g$=10m$ $s^{-2})$

• A. $100N$
• B. $1N$
• C. $20N$
• D. $10N$

Answer 1

Answer: (D)

$10N$

Answer is D.

Buoyancy force can be calculated with the equation $Fb=Vs\times D\times g$, where $Fb$ is the buoyancy force, $Vs$ is the submerged volume, $D$ is the density of the fluid the object is submerged in, and g is the force of gravity.

In this case, the weight of the ball is 4 kg and the density of the ball is

$4000kg/m^3$. Therefore the volume is given as $V=\frac{m}{d}=\frac{4}{4000}{m}^3$. Substituting the given values in the equation, we get,
$Fb=VsDg=\frac{4}{4000}{m}^3\times 1000kg/m^3\times 10m/s^2=10N$.
Hence, the force of buoyancy is 10 N.