Question

How much thurst is exerted by a spherical object of radius $7cm$ and density $0.21gc{m}^{-3}$ placed on a table?

• A. $0.20184N$
• B. $0.30184N$
• C. $4.0184N$
• D. $2.96N$

Answer 1

The correct option is B $0.30184N$

Radius of the sphere,

$\left(r\right)=7cm$
Density of the sphere

$\left(d\right)=0.21gc{m}^{-3}$
Thrust$\left(T\right)=mg$
Let us first calculate the mass of the sphere-
$\text{Mass}=\text{volume}\times \text{density}$

$\Rightarrow M=\frac{4}{3}\pi r^3\times d$

$\Rightarrow M=\frac{4}{3}\pi (7{)}^3\times 0.021$

$\Rightarrow M=\frac{4}{3}\times 343\times 0.21=301.84g$

$\Rightarrow M=301.84\times \frac{1}{1000}kg$

$\Rightarrow M=0.30184kg$

Now, thrust-

$T=0.30184\times 9.8N$

$\Rightarrow T=2.96N$
Therefore, force exerted by the sphere is 2.96 N