Question

A tunnel is dug along a chord of the earth at a perpendicular distance R/2 from the earth's centre. The wall of the tunnel may be assumed to be frictionless. Find the force exerted by the wall on a particle of mass m when it is at a distance x from the centre of the tunnel.

Answer 1

Let d be the distance from centre of earth to man ‘m’ then

M be the mass of the earth, M' the mass of the sphere of radius d/2.