On the surface of a planet?

Question

that is similar to Earth, there is a 3.5 kg mass that weighs 34.3 N.

A) Calculate the mass o the planet in kg
B) Calculate the average density of the planet in kg/m^3

Radius of the planet is roughly 7.4 x 10^6m
G = 6.67259 x 10^-11 N . m^2/kg^2

Answer 1

a)
Gravitational force F between two bodies with masses m1 and m2 separated by a distance r is described by the equation
F=G*m1*m2/r^2, where G is a constant with value 6,67*10^(-11) N*m^2.kg^2.

We know that F=34.3 N and m2 = 3.5kg and r = 7.4*10^6 m
Substituting we get
m1=8.05*10^24 kg

b)

Density d = m / V
Since the planet is a sphere its volume is V=(4/3)*Pi*R^3

So d = 4740 kg/m^3