A narrow hole is drilled through the centre of earth (mass M kg and radius R m). Now consider a particle of mass m which is inside the hole at a distance r m from the centre. (a) Show that p3 M, = M- R3 where M, is the mass of a smaller sphere with radius r inside the earth. Hint: Assume the earth is a uniform sphere and that its density is the same every- where.

A narrow hole is drilled through the centre of earth (mass M kg and radius R m). Now consider a particle of mass m which is inside the hole at a distance r m from the centre. (a) Show that p3 M, = M- R3 where M, is the mass of a smaller sphere with radius r inside the earth. Hint: Assume the earth is a uniform sphere and that its density is the same every- where.