# A stone is dropped freely into a tunnel along the diameter of the earth. When it reaches the center of earth then it has only

a) Potential energy b) Kinetic energy c) weight d) none of there

As it reaches center of earth $g=0$ and it has zero potential energy.
So it does not have weight
It has aquired the kinetic energy due to the loss of potential weight
Hence b is the correct answer
edited Jul 2, 2014