and ρ is the density. On the other hand the · Part 4

a point outside the earth, the force of gravitation on a particle directed towards the centre of the earth is G M m ( . ) where M E = mass of earth, m = mass of the particle and r its distance from the centre of the earth. If we now calculate the work done in lifting a particle from r = r to r = r ( r > r ) along a vertical path, we get instead of Eq. ( .