$(a)$ The Earth is acted upon by the gravitation of the Sun,yet it does not fall into the Sun. Why?
$(b)$ An object of mass $500 \, g$ is dropped from a tower of height $5 \, m$. Calculate its momentum when it touches the ground (given $g = 10 \, m s^{-2}$).

(N/A) This is because the gravitational force of attraction between the Sun and the Earth provides the necessary centripetal force for the Earth's orbital motion.
$(b)$ Given: Mass $m = 500 \, g = 0.5 \, kg$,Height $h = 5 \, m$,Acceleration due to gravity $g = 10 \, m s^{-2}$,Initial velocity $u = 0$.
Using the third equation of motion: $v^2 - u^2 = 2gh$
$v^2 - 0 = 2 \times 10 \times 5 = 100$
$v = \sqrt{100} = 10 \, m s^{-1}$
Momentum $p = m \times v$
$p = 0.5 \, kg \times 10 \, m s^{-1} = 5 \, kg \, m s^{-1}$.