Give reason:
$(a)$ Value of '$g$' is not constant on Earth.
$(b)$ Objects with different masses take the same time to fall from a fixed height.
$(c)$ '$G$' is known as the universal gravitational constant.

(N/A) The acceleration due to gravity is given by the expression $g = \frac{GM}{R^2}$.
This depends upon the radius of the Earth $(R)$. Since the Earth is not a perfect sphere and its radius varies from the poles to the equator,the value of $g$ is not constant everywhere. Additionally,$g$ varies with altitude and depth.
$(b)$ The acceleration due to gravity $(g)$ acting on a falling body is given by $g = \frac{GM}{R^2}$.
This expression shows that $g$ does not depend on the mass of the falling object $(m)$,but only on the mass of the planet $(M)$ and the distance from its center $(R)$. Therefore,all objects fall with the same acceleration,regardless of their mass,and take the same time to fall from a fixed height in a vacuum.
$(c)$ '$G$' is known as the universal gravitational constant because its value remains the same at all places in the universe and is independent of the nature of the medium or the bodies involved.