Suppose that F is an inverse square force field, that is,

Fsrd = cr / |r|3

for some constant c, where r = xi+ yj + zk.

a. Find the work done by F in moving an object from a point P1 along a path to a point P2 in terms of the distances d1 and d2 from these points to the origin.
b. An example of an inverse square field is the gravitational field F = -(mMG)r/|r|3. Use part (a) to find the work done by the gravitational field when the earth moves from aphelion.