At the top of its path,a projectile:

State the universal law of gravitation. Write the $SI$ unit of $G$. The gravitational force between two objects is $100 \, N$. How should the distance between the objects be changed so that the force between them becomes $50 \, N$?

Prove that if a body is thrown vertically upwards,then the time of ascent is equal to the time of descent.

State whether the following statement is True or False:
The acceleration of a body thrown vertically upward is numerically the same as the acceleration of a body falling downward,but opposite in sign.

$A$ boy drops a ball from a cliff $122.5 \, m$ high.
Find:
$(i)$ How long does it take the ball to fall to the ground?
$(ii)$ How far does it fall in the first three seconds?
$(iii)$ How fast is it going at the end of three seconds?

$A$ body weighs $63 \, N$ on the surface of the earth. What is the gravitational force on it due to the earth at a height equal to half the radius of the earth (in $, N$)? (Given: Mass of the earth $= 6 \times 10^{24} \, kg$ and radius of the earth $= 6.4 \times 10^{6} \, m$)