# Newton law of universal gravitation

1. The problem statement, all variables and given/known data

Having problems on the method of calculating the acceleration due to gravity of the planet.

A certain planet has a diameter of 1715 km and a density of 5254 kg/m³. The planet has a moon that orbits every 4.46 earth-days.
What is the acceleration due to gravity associated with this planet? Answer in units of miles/hour

2. Relevant equations

V = (4/3)*∏*(r)^3

F = (G *M1*m2)/(r^2)
G – gravitational constant

F = (m)*(v^2)/(r)
V–velocity

3. The attempt at a solution

so after utilizing half the diameter given as the radius the formula for volume was used to calculate the volume of this planet. since density = mass/volume the equation was rearranged to find the mass of the planet. i am a bit stuck here since i find it difficult using the information for the orbit of the planet into this problem. any insights towards the solution for the acceleration would be appreciated.

http://ift.tt/1fYx6ey