Question

Triton is a satellite of Neptune and has a radius of 5.5 km. What is the mass of Triton if the gravitational force between Triton and a 2.5 kg boulder on its surface is 1.7 x 10-2 N?

Answer 1

Question 30803

According to Newton's Law of gravitation, gravitational force between two objects of mass $M$ and $m$ is $F = G M \frac{m}{R^2}$. Hence, knowing the distance between boulder and center of Triton (radius of Triton), one might express mass of Triton in terms of latter ones:

$$M_{Triton} = \frac{F \cdot R^2}{G \cdot m} = 3.08 \cdot 10^{15} \, \text{kg} \quad (G = 6.67 \cdot 10^{-11})$$