Find the percentage decrease in weight of a body, when taken 16 km below the surface of the earth. Take radius of the earth as 6400 km.

Here, R = 6400 km; x = 16 kmThe value of acceleration due to gravity at a depth x,         g′=g1−xR=g1−166,400=399400g∴ g−g′=g−399400g=1400g=2.5×10−3gIf m is mass of the body, then mg and mg' will be respectively weight of the body on the surface of earth and at a depth of h below the surface of the earth. Then, % decrease in the weight of the body=mg−mg′mg×100=g−g′g×100=2.5×10−3gg×100=0.25%