Question:
The weight of an object at the centre of the earth of radius $R$ is
(a) zero
(b) infinite
(c) $R$ times the weight at the surface of the earth
(d) $1 / R^{2}$ times the weight at surface of the earth.
Solution:
(a) Explanation: $W=m g$. The value of ' $g$ ' at the centre of earth is zero.