1. The problem statement, all variables and given/known data A tunnel is drilled from the surface of the earth(mass assumed to be M and radius to be R) to its center . A body of mass m is dropped from the surface to the center through the tunnel. What will be the velocity with which the body of mass m will hit the tunnel. 2. Relevant equations Loss in PE = Gain In KE Loss in PE = PE at surface - PE at center of earth. = |-GMm/R - 0| 1/2 mv = |-GMm/R| v = √(2GM/R) 3. The attempt at a solution But in a textbook , the PE at the center of earth is given to be -(3/2) (GMm/R) what is the right way of approaching the problem.