Gravitational force between 2 particles

[clope023]

Homework Statement

A uniform, solid, 1900kg sphere has a radius of 5.00m. Find the gravitational force this sphere exerts on a 1.50kg point mass placed at the following distances from the center of the sphere: (a) 5.01m , and (b) 2.45m.

Homework Equations

Fg = GMm/r^2

volume of sphere = (4/3)piR^3

density of sphere = M/volume

ratio of point mass to shere:

M/msphere = (4/3piRM^3)/(4/3piRsphere^3)

Mmass = msphere(Rmass/Rsphere)^3

G(M)(mmass)/r^2 = Gmass(msphere(rmass/rsphere)^3)/Rsphere^2

= G(mmass)(msphere)rmass/rsphere

The Attempt at a Solution

Fg = G(1900)(1.50)(5.01)/5^2 = 3.8x10^-7

Fg = G(1900)(1.50)/5^2 = 8x10^-8

nothing, I'm not sure what I'm doing wrong, any help is greatly appreciated.

 

[Snazzy]

Homework Statement

A uniform, solid, 1900kg sphere has a radius of 5.00m. Find the gravitational force this sphere exerts on a 1.50kg point mass placed at the following distances from the center of the sphere: (a) 5.01m , and (b) 2.45m.

Homework Equations

Fg = GMm/r^2

volume of sphere = (4/3)piR^3

density of sphere = M/volume

ratio of point mass to shere:

M/msphere = (4/3piRM^3)/(4/3piRsphere^3)

Mmass = msphere(Rmass/Rsphere)^3

G(M)(mmass)/r^2 = Gmass(msphere(rmass/rsphere)^3)/Rsphere^2

= G(mmass)(msphere)rmass/rsphere

The Attempt at a Solution

Fg = G(1900)(1.50)(5.01)/5^2 = 3.8x10^-7

Fg = G(1900)(1.50)/5^2 = 8x10^-8

nothing, I'm not sure what I'm doing wrong, any help is greatly appreciated.

Where are the 5^2 coming from?