A particle is kept on the surface of a uniform sphere of mass 1000 kg and radius 1 m. The work done per unit mass against the gravitational force between them is

[G = 6.67 $$\times$$ 10$$^{-11}$$ Nm$$^2$$ kg$$^{-2}$$]

The acceleration due to gravity at a height (1/20)th of the radius of Earth above the Earth's surface is 9 ms$$^{-2}$$. Its value at an equal depth below the surface of earth is