1. The problem statement, all variables and given/known data Consider a simple model for the interior of the Earth: there is a spherical iron core with constant mass density ρ0 and radius a; outside the core is "rock" with constant density ρ1. Use these values for the densities: ρ0= 8.90×103 kg/m3 and ρ1= 3.80×103 kg/m3. The radius of the Earth is R = 6.40×106 m. Calculate the radius a of the iron core. Derive the graviational field g(r) as a function of r. Find g(a). 2. Relevant equations [itex]\Phi[/itex]=-G[itex]\int[/itex]([itex]\rho[/itex](r')/r)dv' g=-[itex]\nabla[/itex][itex]\Phi[/itex] 3. The attempt at a solution I really am unsure as where to go with this one. I have the mass of the core as a ratio of the densities, but from there I am stuck.