Question

Krypton (planet of superman) has mass twice that of earth and radius thrice that of earth. What would be the weight of superman on krypton if his weight on earth is $900\text{N}?$

• A. $900\text{N}$
• B. $1800\text{N}$
• C. $200\text{N}$
• D. $450\text{N}$

Answer 1

The correct option is C $200\text{N}$

We know, acceleration due to gravity,
$g=\frac{GM}{R^2}$

On Krypton,
$g^{{}^{\prime }}=\frac{G\left(2M\right)}{(3R{)}^2}=\frac{2GM}{9R^2}=\frac{2}{9}g$

Given, weight on earth, $W=mg=900\text{N}$

So, weight on Krypton, $W^{{}^{\prime }}=m{g}^{{}^{\prime }}=\frac{2}{9}mg$
$\Rightarrow W^{{}^{\prime }}=\frac{2}{9}\times 900=200\text{N}$