Question

If a bag of rice weighs $30\text{kg}$ on Earth, what is the weight of the rice bag on the planet Neptune? Take the mass of Neptune to be ${10}^{26}\text{kg}$, and its radius to be $25\times {10}^6\text{m}$.

• A. $110\text{N}$
• B. $320\text{N}$
• C. $150\text{N}$
• D. $60\text{N}$

Answer 1

The correct option is B $320\text{N}$

Given:
Mass of the rice bag, $m_{rb}=30\text{kg}$
Mass of Neptune, $M_{nep}={10}^{26}\text{kg}$
Radius of Neptune, $r_{nep}=25\times {10}^6\text{m}$

From the universal law of gravitation,
Weight of the rice bag on Neptune:
$W_{rb}=\frac{G{M}_{nep}{m}_{rb}}{r_{nep}^2}$
$W_{rb}=\frac{6.67\times {10}^{-11}\times {10}^{26}\times 30}{(25\times {10}^6{)}^2}$
$W_{rb}\approx \frac{2\times {10}^{17}}{625\times {10}^{12}}=320\text{N}$