Question

The radius of earth is about $6400km$ and that of mars is $3200km$. The mass of the earth is about $10$ times mass of mars. An object weighs $200N$ on the surface of earth. Its weight on the surface of mars will be

• A. 20 N
• B. 8 N
• C. 80 N
• D. 40 N

Answer 1

Answer: (C)

Radius of earth $\left(R_e\right)=6400km$;
Radius of mars $\left(R_m\right)=3200km$;
Mass of earth $\left(M_e\right)=10$ and weight of the object on earth $\left(W_e\right)=200N$.
$\frac{W_m}{W_e}=\frac{m{g}_m}{m{g}_e}=\frac{M_m}{M_e}\times {\left(\frac{R_e}{R_m}\right)}^2=\frac{1}{10}\times (2{)}^2$
$=\frac{4}{10}=\frac{2}{5}$
or $W_m=W_e\times \frac{2}{5}$
$=200\times 0.4=80N$