The Gravitational Force on a Particle inside a Concentric Sphere and Shell

[h4d]

Homework Statement

A uniform solid sphere is inside and concentric with a spherical shell.

M1=133kg ---mass of shell
R1=2.42m ---radius of shell

M2=278kg --mass of sphere
R2=1.16m --radius of sphere

a) Find the magnitude of the gravitational force exerted by the sphere and spherical shell on a particle of mass 6 kg located at a distance 0.56 m from the center of the sphere and spherical shell.

b) Find the magnitude of the gravitational force exerted by the sphere and spherical shell on a particle of mass 6 kg located at a distance 1.66 m from the center of the sphere and
spherical shell.

c)Find the magnitude of the gravitational force exerted by the sphere and spherical shell on a particle of mass 6 kg located at a distance 2.84 m from the center of the sphere and spherical shell.

Homework Equations

F=GMm/r^2

The Attempt at a Solution

For the first one, I thought that the answer should be zero because I believed that the force on point masses inside a sphere/shell was zero.

I'm not sure how to begin with the rest because I think I'm overlooking something in the first part.

 

[ehild]

The gravitational force at distance r from a homogeneous sphere is the same as if all the mass contained in a sphere of radius r concentrated in the centre. So the gravitational force at 0.56 m from the centre is not zero.

ehild