(a) Define gravitational field intensity at a point in space.
(b) Write the expression for the magnitude of the gravitational field intensity produced by an isolated point mass M at a distance r from it.
(c) Explain clearly how the direction of the gravitational field vector is decided for
(i) a single point mass and
(ii) a system of two point masses located on the same straight line.
(d) Give a qualitative argument to show that the gravitational field intensity at every interior point of a thin, uniform spherical shell is zero.