Homework Help: Conform/help with calc solution

1. Nov 29, 2007

allenmatt59

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

Newton’s law of gravitation states that the force between two masses m1
and m2 at a distance r apart is F = Gm1m2/r2 .
(a) Find the magnitude of the gravitational force exerted by a solid hemisphere
of radius a and constant density  on a point mass located at
the center of the base of the hemisphere.
(b) A particle of mass m is placed at the center of one base of a circular
cylindrical shell of inner radius r1, outer radius r2, height h, and
constant density . Find the force of gravitational attraction exerted
by the cylinder on the particle.

3. The attempt at a solution

because the only force which would act on the bottom center of the hemisphere is pointed straight down. the force would be represented in a negative direction (-x/||x||). therefore f(x)=-mMGx/||x3||. ||x||=sqrt(x2+y2+z2).
because the force is coming only from the z direction F(x,y,z)=-mMGz/((z2)to the 3/2power)
is there someone to conform that.