A tunnel is dug along the diameter of the earth (radius R and mass  M). There is a particle of mass 'm'  at the centre of the tunnel. The minimum velocity given to the particle so that it just reaches to the surface of the earth is

Given Mass of Earth =MRadius of Earth =RLet the minimum speed imparted to the particle of mass m  so that it just reaches surface of earth is  v.Applying the principle of conservation of energy,12mv2+−32GMRm=−GMRm+0  12v2=−GMR+32GMR=GMR , we get  v=GMR.Therefore, the correct answer is (A).