Question

What is the weight of a 70 kg body on the surface of a planet whose mass is $\frac{1}{7}$ th that of earth and radius is half of earth?

• A. 20 kg
• B. 40 kg
• C. 70 kg
• D. 140 kg

Answer 1

The correct option is B 40 kg

$g_e=\frac{GM}{R^2}$ (Gravitational acceleration of earth)

$g^{\prime }=\frac{GM}{7R^2}\times 4$ (Gravitational acceleration of planet)

Weight on that planet $W^{\prime }=m{g}^{\prime }$

$=m\times \frac{4GM}{7R^2}$

$=\frac{4}{7}\times \frac{GMm}{R^2}$

$=\frac{4}{7}\times mg=\frac{4}{7}W$

$=\frac{4}{7}\times 70=40kg$